# By how much does Haumea's fast rotation affect its surface gravity?

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The equation for surface gravity is $$frac{GM}{r^2}$$ but I'm not sure how to include the effects from its rotation.

The numbers are going to be approximate because Haumea's size is uncertain. It may have a ring. If it does, then it's smaller, if it doesn't, then it's larger.

The formula is simple enough. For force: $$F= frac {m v^2} {r}$$ where v is the rotational velocity and r is the same r in the gravitational formula. or $$frac {v^2} {r}$$ if you want the reverse acceleration.

Haumea has a rotational period of 3.915 hours or 14,090 seconds (I'm rounding) and an average radius of 780,000 meters (assuming it has a ring, I'm going to go with that assumption), but an estimated equatorial radius of about 1,050,000 meters and that's the number we need. Divide the larger radius by number of seconds, multiply by 2 Pi and the velocity is 468.2 m/s. A tiny bit faster than Earth's equatorial velocity.

Some Maths, the lifting force on the equator is $$frac {468.2^2} {1,050,000}$$ = $$0.208 frac {m}{s^2}$$, slightly over half it's listed equatorial surface gravity of $$0.401 frac {m}{s^2}$$.

That's a pretty high ratio. Possibly the highest in our solarsystem for objects that are massive enough to be spheroid shaped by their mass and gravity. There are asteroids that are thought to effectively have negative gravity at their equator, held together by the stickiness of the material, but those are a lot smaller.

## Surface gravity

The surface gravity, g, of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in order not to disturb the system, has negligible mass.

Surface gravity is measured in units of acceleration, which, in the SI system, are meters per second squared. It may also be expressed as a multiple of the Earth's standard surface gravity, g = 9.80665 m/s². [1] In astrophysics, the surface gravity may be expressed as log g, which is obtained by first expressing the gravity in cgs units, where the unit of acceleration is centimeters per second squared, and then taking the base-10 logarithm. [2] Therefore, the surface gravity of Earth could be expressed in cgs units as 980.665 cm/s², with a base-10 logarithm (log g) of 2.992.

The surface gravity of a white dwarf is very high, and of a neutron star even higher. The neutron star's compactness gives it a surface gravity of up to 7 × 10 12 m/s² with typical values of order 10 12 m/s² (that is more than 10 11 times that of Earth). One measure of such immense gravity is that neutron stars have an escape velocity of around 100,000 km/s, about a third of the speed of light. For black holes, the surface gravity must be calculated relativistically.

• The shape of Haumea is believed to be the result of its rapid rotation.
• The International Astronomical Union (IAU) classified Haumea as a dwarf planet on September 17th, 2008.
• Haumea is the newest discovered planet in our solar system. It has two moons orbiting it called Hi’iaka and Namaka, respectively.
• The moons of Haumea are thought to be the result of a collision from a space object.
• Every day on Haumea lasts 3.9 Earth hours!
• Scientists have confirmed that the dwarf planet is made from a rock with a thick coating of ice, but what they can’t understand yet are its origins.
• The third brightest object in the Kuiper belt is Haumea!
• The dwarf planet Haumea has a red spot.

## Haumea

Located in the Kuiper Belt beyond Neptune&rsquos orbit, the dwarf planet Haumea is an oval-shaped object with a radius of about 385 miles (just under 10 times smaller than Earth), and two moons, Namaka and Hi&rsquoiaka. A day on Haumea lasts only four Earth hours, making it one of the fastest rotating large objects in our solar system.

Overview Originally designated 2003 EL61 (and nicknamed Santa by one discovery team), Haumea resides in the Kuiper belt and is roughly the same size as Pluto. Haumea is one of the fastest rotating large objects in our solar system. Its fast spin distorts Haumea's shape, making this dwarf planet look like a football.

### Discovery

Two teams claim credit for discovering of Haumea citing evidence from observations made in 2003 and 2004. The International Astronomical Union&rsquos Gazetteer of Planetary Nomenclature lists the discovery location as Sierra Nevada Observatory in Spain on Mar. 7, 2003, but no official discoverer is listed.

Haumea was named after the Hawaiian goddess of fertility.

### Size and Distance

With a radius of about 385 miles (620 kilometers), Haumea is about 1/14 the radius of Earth. If Earth were the size of a nickel, Haumea would be about as big as a sesame seed.

From an average distance of 4,010,000,000 miles (6,452,000,000 kilometers), Haumea is 43 astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 6 hours to travel from the Sun to Haumea.

### Orbit and Rotation

Haumea takes 285 Earth years to make one trip around the Sun. As Haumea orbits the Sun, it completes one rotation every 4 hours, making it one of the fastest rotating large objects in our solar system.

It is possible a massive impact billions of years ago set off Haumea's spin and created its moons.

### Formation

Dwarf planet Haumea is a member of a group of objects that orbit in a disc-like zone beyond the orbit of Neptune called the Kuiper Belt. This distant realm is populated with thousands of miniature icy worlds which formed early in the history of our solar system about 4.5 billion years ago. These icy, rocky bodies are called Kuiper Belt objects, transneptunian objects, or plutoids.

### Structure

Astronomers believe Haumea is a made of rock with a coating of ice.

### Surface

We know very little about Haumea's surface.

### Atmosphere

We know very little about Haumea's atmosphere.

### Potential for Life

The surface of Haumea is extremely cold, so it seems unlikely that life could exist there.

### Moons

Haumea has two known moons: Namaka is the inner moon, and Hi'iaka is the outer moon. Both are named for the mythological daughters of Huamea. Hi'aka is the patron goddess of the island of Hawaii and of hula dancers. Namaka is a water spirit in Hawaiian mythology.

### Rings

Haumea is the first known Kuiper Belt Object to have rings. Scientists announced the discovery in 2017 after watching the dwarf planet pass in front of a star.

### Magnetosphere

Scientists do not think Haumea has a magnetosphere.

### Exploration

Everything we know about Haumea is from observations with ground-based telescopes from around the world.

## 10 Facts About the Dwarf Planet Haumea

In terms of sheer weirdness, few objects in the solar system can compete with the dwarf planet Haumea. It has a strange shape, unusual brightness, two moons, and a wild rotation. Its unique features, however, can tell astronomers a lot about the formation of the solar system and the chaotic early years that characterized it. Here are a few things you need to know about Haumea, the tiny world beyond Neptune.

#### 1. THREE HAUMEAS COULD FIT SIDE BY SIDE IN EARTH.

Wikimedia Commons // CC-BY-SA-3.0

Haumea is a trans-Neptunian object its orbit, in other words, is beyond that of the farthest ice giant in the solar system. Its discovery was reported to the International Astronomical Union in 2005, and its status as a dwarf planet—the fifth, after Ceres, Eris, Makemake, and Pluto—was made official three years later. Dwarf planets have the mass of a planet and have achieved hydrostatic equilibrium (i.e., they're round), but have not "cleared their neighborhoods" (meaning their gravity is not dominant in their orbit). Haumea is notable for the large amount of water ice on its surface, and for its size: Only Pluto and Eris are larger in the trans-Neptunian region, and Pluto only slightly, with a 1475-mile diameter versus Haumea's 1442-mile diameter. That means three Haumeas could fit sit by side in Earth—and yet it only has 1/1400th of the mass of our planet.

#### 2. HAUMEA'S DISCOVERY WAS CONTROVERSIAL.

There is some disagreement over who discovered Haumea. A team of astronomers at the Sierra Nevada Observatory in Spain first reported its discovery to the Minor Planet Center of the International Astronomical Union on July 27, 2005. A team led by Mike Brown from the Palomar Observatory in California had discovered the object earlier, but had not reported their results, waiting to develop the science and present it at a conference. They later discovered that their files had been accessed by the Spanish team the night before the announcement was made. The Spanish team says that, yes, they did run across those files, having found them in a Google search before making their report to the Minor Planet Center, but that it was happenstance—the result of due diligence to make sure the object had never been reported. In the end, the IAU gave credit for the discovery to the Spanish team—but used the name proposed by the Caltech team.

#### 3. IT'S NAMED FOR A HAWAIIAN GODDESS.

In Hawaiian mythology, Haumea is the goddess of fertility and childbirth. The name was proposed by the astronomers at Caltech to honor the place where Haumea's moon was discovered: the Keck Observatory on Mauna Kea, Hawaii. Its moons—Hi'iaka and Namaka—are named for two of Haumea's children.

#### 4. HAUMEA HAS RINGS—AND THAT'S STRANGE.

Haumea is the farthest known object in the solar system to possess a ring system. This discovery was recently published in the journal Nature. But why does it have rings? And how? "It is not entirely clear to us yet," says lead author Jose-Luis Ortiz, a researcher at the Institute of Astrophysics of Andalusia and leader of the Spanish team of astronomers who discovered Haumea.

#### 5. HAUMEA'S SURFACE IS EXTREMELY BRIGHT.

In addition to being extremely fast, oddly shaped, and ringed, Haumea is very bright. This brightness is a result of the dwarf planet's composition. On the inside, it's rocky. On the outside, it is covered by a thin film of crystalline water ice [PDF]—the same kind of ice that's in your freezer. That gives Haumea a high albedo, or reflectiveness. It's about as bright as a snow-covered frozen lake on a sunny day.

#### 6. HAUMEA HAS ONE OF THE SHORTEST DAYS IN THE ENTIRE SOLAR SYSTEM.

If you lived to be a year old on Haumea, you would be 284 years old back on Earth. And if you think a Haumean year is unusual, that's nothing next to the length of a Haumean day. It takes 3.9 hours for Haumea to make a full rotation, which means it has by far the fastest spin, and thus shortest day, of any object in the solar system larger than 62 miles.

#### 7. HAUMEA'S HIGH SPEED SQUISHES IT INTO A SHAPE LIKE A RUGBY BALL.

As a result of this tornadic rotation, Haumea has an odd shape its speed compresses it so much that rather than taking a spherical, soccer ball shape, it is flattened and elongated into looking something like a rugby ball.

#### 8. HIGH-SPEED COLLISIONS MAY EXPLAIN HAUMEA'S TWO MOONS.

Ortiz says there are several mechanisms that can have led to rings around the dwarf planet: "One of our favorite scenarios has to do with collisions on Haumea, which can release material from the surface and send it to orbit." Part of the material that remains closer to Haumea can form a ring, and material further away can help form moons. "Because Haumea spins so quickly," Ortiz adds, "it is also possible that material is shed from the surface due to the centrifugal force, or maybe small collisions can trigger ejections of mass. This can also give rise to a ring and moons."

#### 9. ONE MOON HAS WATER ICE—JUST LIKE HAUMEA.

Ortiz says that while the rings haven't transformed scientists' understanding of Haumea, they have clarified the orbit of its largest moon, Hi'iaka—it is equatorial, meaning it circles around Haumea's equator. Hi'iaka is notable for the crystalline water ice on its surface, similar to that on its parent body.

#### 10. TRYING TO SEE HAUMEA FROM EARTH IS LIKE TRYING TO LOOK AT A COIN MORE THAN 100 MILES AWAY.

It's not easy to study Haumea. The dwarf planet, and other objects at that distance from the Sun, are indiscernible to all but the largest telescopes. One technique used by astronomers to study such objects is called "stellar occultation," in which the object is observed as it crosses in front of a star, causing the star to temporarily dim. (This is how exoplanets—those planets orbiting other stars—are also often located and studied.) This technique doesn't always work for objects beyond the orbit of Neptune, however astronomers must know the objects' orbits and the position of the would-be eclipsed stars to astounding levels of accuracy, which is not always the case. Moreover, Ortiz says, their sizes are oftentimes very small, "comparable to the size of a small coin viewed at a distance of a couple hundred kilometers."

## The dwarf planet Haumea

Artist’s impression of the dwarf planet Haumea and its moons, Hi’aka and Namaka. Credit: NASA

The Trans-Neptunian region has become a veritable treasure trove of discoveries in recent years. Since 2003, the dwarf planets and "plutoids" of Eris, Sedna, Makemake, Quaoar, and Orcus were all observed beyond the orbit of Pluto. And in between all of these, Haumea – that odd, oblong-shaped dwarf planet that has its own system of moons – was also discovered.

In addition to being the largest member of its particular family of Trans-Neptunian Objects (TNOs), Haumea is unique amongst known dwarf planets. This is due to its elongation, an unusually rapid rotation, two known moons, high density, and high albedo – all of which make Haumea something of an oddity when it comes to dwarf planets.

While bodies that are designated as dwarf planets tend to attract their share of controversy, dissension over Haumea began as soon as it was discovered. In fact, two teams claim credit for its discovery: Mike Brown and his team at Caltech and Jose Luis Ortiz Moreno and his team from the Instituto de Astrofísica de Andalucía at Sierra Nevada Observatory in Spain.

The former discovered Haumea in December of 2004 from images they had taken on May 6th, 2004 from the W.M. Keck Observatory. They published an online abstract about their discovery on July 20th, 2005, and announced their discovery at a conference in September of that year. Meanwhile, Ortiz and his team emailed the IAU Minor Planet Center of the discovery of Haumea on July 27th, 2005, claiming they had found it on images taken from March 7th to 10th, 2003.

The IAU announcement on September 17th, 2008, that Haumea had been accepted as a dwarf planet, did not mention a discoverer. The location of discovery was listed as the Sierra Nevada Observatory of the Spanish team, but the chosen name, Haumea, was proposed by the Caltech team.

The name Haumea comes from Hawaiian mythology, specifically from the goddess of fertility who is also the matron goddess of the island of Hawaii where the W. M. Keck Observatory is located. Hence, the name was not only consistent with IAU guidelines – that classical Kuiper Belt Objects (KBOs) be given names of mythological beings associated with creation – but was also an homage to the facility that made the discovery.

Ortiz's team had proposed "Ataecina", named for the ancient Iberian goddess of Spring but not meet the IAU requirements since she is not a creation goddess, and hence was rejected. Until it was given a permanent name, the Caltech discovery team used the nickname "Santa" among themselves, because they had discovered Haumea on December 28th, 2004, just after Christmas.

Because the Spanish team had filed their claim with the Minor Planet Center first, Haumea was given the provisional designation 2003 EL61 (based on the date of the Spanish discovery image) on July 29th, 2005.

Calculating Haumeau's size, mass and density is somewhat complicated. Whereas it is large enough and bright enough for its albedo (and thus its size) to be measured, the calculations of its dimensions are made difficult by its rapid rotation. However, several ellipsoid-model calculations have been conducted using the Keck telescopes, the Spitzer Space Telescope, and the Herschel Space Telescope that have provided estimates.

The first calculations, conducted by Brown et al., provided the approximate dimensions of 2,000 x 1,500 x 1,000 km. Meanwhile, the Spitzer measurements gave it a diameter of 1050 – 1400 km, while subsequent light-curve analyses suggested an equivalent circular diameter of 1,450 km. In 2010 an analysis of measurements taken by Herschel Space Telescope together with the older Spitzer Telescope measurements yielded a new estimate of

Keck image of 2003 EL61 Haumea, with moons Hi’iaka and Naumaka. Credit: CalTech/Mike Brown et al.

These independent size estimates overlap at an average geometric mean diameter of roughly 1,400 km. In essence, this means that Haumea is comparable in diameter to Pluto along its longest axis and about half that at its poles. It's mass, meanwhile, is estimated to be approximately 4.0 ×1021 kg – one-third the mass of Pluto and 1/1400th that of Earth.

This makes Haumea one of the largest trans-Neptunian objects discovered, smaller than Eris, Pluto, probably Makemake, and possibly 2007 OR10, but larger than Sedna, Quaoar, and Orcus. Combined with estimates of its density, Haumea is massive enough to have achieved hydrostatic equilibrium. Although Haumea appears to be far from spherical, its ellipsoidal shape is thought to result from its rapid rotation.

Haumea has a typical orbit for a classical KBO, with an eccentric orbit that takes it from 34.952 AU (5.23 trillion km) at perihelion to 51.483 AU (7.7 trillion km) at aphelion. Also consistent with other KBOs, it has an orbital period of 284 Earth years, an orbital inclination of 28°, and completes a sidereal rotation every 3.9 hours (0.163 Earth days).

Much like its size, Haumea's rotation and the amplitude of its light curve make judging its composition rather difficult. If its density were consistent with Pluto and other KBOs (2.0 g/cm³) then its rapid rotation would have elongated it to a greater extent than current estimates allow for. As such, Haumea's density is believed to range between 2.6 – 3.3 g/cm³, which is comparable to Earth's Moon (also 3.3 g/cm³).

Haumea's possible density covers the values for silicate minerals such as olivine and pyroxene, which make up many of the rocky objects in the Solar System. This suggests that the bulk of Haumea is rock covered with a relatively thin layer of ice. It is possible that a thicker ice mantle that is more typical of Kuiper belt objects existed in the past, but was blasted off during the impact that formed the Haumean collisional family.

Haumea is as bright as snow, with an high albedo that is consistent with crystalline ice. Spectral modelling of the surface suggested that 66% to 80% of the Haumean surface appears to be pure crystalline water ice, with the possible presence of hydrogen cyanide or phyllosilicate clays. Inorganic cyanide salts such as copper potassium cyanide may also be present.

A large dark red area on Haumea's bright white surface, possibly an impact feature, has also been observed which could indicate an area rich in minerals and organic (carbon-rich) compounds – or possibly a higher proportion of crystalline ice. Thus Haumea may have a mottled surface similar to that of Pluto.

Haumea has been classified as a plutoid and dwarf planet residing beyond Neptune's orbit. This classification means that it is presumed to be massive enough to have been rounded by its own gravity, but not to have cleared its neighborhood of similar objects.

Although Haumea appears to be far from spherical, its ellipsoidal shape is thought to result from its rapid rotation and not from a lack of sufficient gravity to overcome the compressive strength of its material. Haumea was initially listed as a classical Kuiper Belt Object in 2006 by the Minor Planet Center, but that has since been revised.

Haumea has two known moons, which are named after the daughters of the Hawaiian goddess – Hi'iaka and Namaka. Both were discovered in 2005 by Brown's team while conducting observations of Haumea at the W.M. Keck Observatory. Hi'iaka, which was initially nicknamed "Rudolph" by the Caltech team, was discovered January 26th, 2005.

It is the outer and – at roughly 310 km in diameter – the larger and brighter of the two, and orbits Haumea in a nearly circular path every 49 days. Infrared observations indicate that its surface is almost entirely covered by pure crystalline water ice. Because of this, Brown and his team have speculated that the moon is a fragment of Haumea that broke off during a collision.

Comparison of Sedna with the other largest TNOs and with Earth (all to scale). Credit: NASA/Lexicon

Namaka, the smaller and innermost of the two, was discovered on June 30th, 2005, and nicknamed "Blitzen". It is a tenth the mass of Hi'iaka and orbits Haumea in 18 days in a highly elliptical orbit. Both moons circle Haumea is highly eccentric orbits. No estimates have been made yet as to their mass.

So far, no missions have been mounted to Haumea and none are currently planned. However, numerous scenarios have been calculated using hypothetical launch dates. For example, if a probe were launched on September 25th, 2025, a flyby mission could take place within 14.25 years, when Haumea would be 48.18 AU from the Sun. Based on a launch date of Nov. 1st, 2026, September 23rd, 2037, and October 29th, 2038, a flyby mission would take 16.45 years to get to Haumea.

So if the budget environment remains stable and scientists decide to make close-up observations of Haumea a priority, a flyby could be taking place no sooner than December of 2039. And with luck, we might learn more about this distant and odd little ball of rock and ice that stands out from its peers.

## A cosmic alignment

Scientists had the chance to learn more about this space oddity when Haumea passed in front of the star URAT1 533-182543 on Jan. 21, 2017. Although objects pass in front of stars quite often, it's difficult to accurately predict the specific time and location of these events, study co-author Pablo Santos Sanz told Space.com. Santos Sanz is an astrophysicist at the Instituto de Astrofísica de Andalucía in Granada, Spain.

Santos Sanz's team coordinated 12 telescopes, from 10 different labs, to observe starlight blocked by Haumea and thus better determine its size and shape. Normally, shadows are larger than the objects that cast them. For instance, you can move your hand closer and farther from a flashlight to make its shadow grow and shrink. But the star was so far from Earth relative to Haumea that it projected the dwarf planet's shadow at full size.

"This is a very powerful technique … to obtain sizes," Santos Sanz said. The researchers discovered that Haumea's longest axis is at least 1,430 miles (2,300 kilometers) across &mdash 17 percent larger than previous estimates.

The more accurate measurements of Haumea enabled the astronomers to calculate many of the dwarf planet's other properties. Factoring in the rotation gave them its 3D shape and volume. Combining this with its mass &mdash derived from the orbits of its moons &mdash yielded Haumea's density. It was lower than previous estimates, Santos Sans said, but was closer to that of other Kuiper Belt objects, like Pluto.

But these new measurements may cost Haumea its dwarf-planet status. Although many planets and dwarf planets are not perfect spheres &mdash Earth, for instance, bulges a bit at the equator &mdash they are all large enough to have become round due to their own gravity. In contrast, most smaller objects don't have enough gravity to overcome their own rigidity, so they end up oddly shaped or lumpy. This criterion is central to the contentious definition of a dwarf planet, and the more accurate picture of Haumea that emerged from the study appears not to meet it.

"I don't know if this will change the definition [of a dwarf planet]," Santos Sanz said. "I think probably yes, but probably it will take time."

Most surprisingly, the scientists learned that Haumea has rings.

The night Haumea crossed in front of the distant star, Santos Sanz and team leader José Luis Ortiz, also of the Instituto de Astrofísica de Andalucía, looked at the new data.

"We started to see something weird in the light curve," Santos Sanz said. The light dimmed just before and after Haumea passed in front of the star, as if something else were obscuring it. "I remember that José Luis, from the first [moments], said, 'OK, this could be a ring,'" Santos Sanz said. Months of scrutiny bore out the scientists' initial suspicions: The results suggest that Haumea's equator is encircled by a 43-mile-wide (70 km) ring of debris located about 620 miles (1,000 km) from the dwarf planet's surface.

"Rings are usually the sign of a collision that happened not too long ago," Yale astronomer David Rabinowitz, who is unaffiliated with the study, told Space.com. For Rabinowitz, this means sometime between several hundred-million years ago and one billion years ago. The search for the rings' origin makes the system that much more interesting, he added. It's another mystery about the dwarf planet begging for an answer.

## Contents

### Discovery Edit

Two teams claim credit for the discovery of Haumea. A team consisting of Mike Brown of Caltech, David Rabinowitz of Yale University and Chad Trujillo of Gemini Observatory in Hawaii discovered Haumea on December 28, 2004 on images they had taken on May 6, 2004. On July 20, 2005, they published an online abstract of a report intended to announce the discovery at a conference in September 2005. [24] At around this time, José Luis Ortiz Moreno and his team at the Instituto de Astrofísica de Andalucía at Sierra Nevada Observatory in Spain found Haumea on images taken on March 7–10, 2003. [25] Ortiz emailed the Minor Planet Center with their discovery on the night of July 27, 2005. [25]

Brown initially conceded discovery credit to Ortiz, [26] but came to suspect the Spanish team of fraud upon learning that the Spanish observatory had accessed Brown's observation logs the day before the discovery announcement.

These logs included enough information to allow the Ortiz team to precover Haumea in their 2003 images, and they were accessed again just before Ortiz scheduled telescope time to obtain confirmation images for a second announcement to the MPC on July 29. Ortiz later admitted he had accessed the Caltech observation logs but denied any wrongdoing, stating he was merely verifying whether they had discovered a new object. [27] Precovery images of Haumea have been identified back to March 22, 1955. [8]

IAU protocol is that discovery credit for a minor planet goes to whoever first submits a report to the MPC (Minor Planet Center) with enough positional data for a decent determination of its orbit, and that the credited discoverer has priority in choosing a name. However, the IAU announcement on September 17, 2008, that Haumea had been named by dual committee established for bodies expected to be dwarf planets, did not mention a discoverer. The location of discovery was listed as the Sierra Nevada Observatory of the Spanish team, [28] [29] but the chosen name, Haumea, was the Caltech proposal Ortiz's team had proposed "Ataecina", the ancient Iberian goddess of spring, [25] which as a chthonic deity would have been appropriate for a plutino.

### Name Edit

Until it was given a permanent name, the Caltech discovery team used the nickname "Santa" among themselves, because they had discovered Haumea on December 28, 2004, just after Christmas. [30] The Spanish team were the first to file a claim for discovery to the Minor Planet Center, in July 2005. On July 29, 2005, Haumea was given the provisional designation 2003 EL61, based on the date of the Spanish discovery image. On September 7, 2006, it was numbered and admitted into the official minor planet catalog as (136108) 2003 EL61.

Following guidelines established at the time by the IAU that classical Kuiper belt objects be given names of mythological beings associated with creation, [31] in September 2006 the Caltech team submitted formal names from Hawaiian mythology to the IAU for both (136108) 2003 EL61 and its moons, in order "to pay homage to the place where the satellites were discovered". [32] The names were proposed by David Rabinowitz of the Caltech team. [22] Haumea is the matron goddess of the island of Hawaiʻi, where the Mauna Kea Observatory is located. In addition, she is identified with Papa, the goddess of the earth and wife of Wākea (space), [33] which, at the time, seemed appropriate because Haumea was thought to be composed almost entirely of solid rock, without the thick ice mantle over a small rocky core typical of other known Kuiper belt objects. [34] [35] Lastly, Haumea is the goddess of fertility and childbirth, with many children who sprang from different parts of her body [33] this corresponds to the swarm of icy bodies thought to have broken off the main body during an ancient collision. [35] The two known moons, also believed to have formed in this manner, [35] are thus named after two of Haumea's daughters, Hiʻiaka and Nāmaka. [34]

The proposal by the Ortiz team, Ataecina, did not meet IAU naming requirements, because the names of chthonic deities were reserved for stably resonant trans-Neptunian objects such as plutinos that resonate 3:2 with Neptune, whereas Haumea was in an intermittent 7:12 resonance and so by some definitions was not a resonant body. The naming criteria would be clarified in late 2019, when the IAU decided that chthonic figures were to be used specifically for plutinos. (See Ataecina § Dwarf planet.)

Haumea has an orbital period of 284 Earth years, a perihelion of 35 AU, and an orbital inclination of 28°. [8] It passed aphelion in early 1992, [36] and is currently more than 50 AU from the Sun. [20] It will come to perihelion in 2133. [36] Haumea's orbit has a slightly greater eccentricity than that of the other members of its collisional family. This is thought to be due to Haumea's weak 7:12 orbital resonance with Neptune gradually modifying its initial orbit over the course of a billion years, [35] [37] through the Kozai effect, which allows the exchange of an orbit's inclination for increased eccentricity. [35] [38] [39]

With a visual magnitude of 17.3, [20] Haumea is the third-brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope. [40] However, because the planets and most small Solar System bodies share a common orbital alignment from their formation in the primordial disk of the Solar System, most early surveys for distant objects focused on the projection on the sky of this common plane, called the ecliptic. [41] As the region of sky close to the ecliptic became well explored, later sky surveys began looking for objects that had been dynamically excited into orbits with higher inclinations, as well as more distant objects, with slower mean motions across the sky. [42] [43] These surveys eventually covered the location of Haumea, with its high orbital inclination and current position far from the ecliptic.

### Rotation Edit

Haumea displays large fluctuations in brightness over a period of 3.9 hours, which can only be explained by a rotational period of this length. [45] This is faster than any other known equilibrium body in the Solar System, and indeed faster than any other known body larger than 100 km in diameter. [40] While most rotating bodies in equilibrium are flattened into oblate spheroids, Haumea rotates so quickly that it is distorted into a triaxial ellipsoid. If Haumea were to rotate much more rapidly, it would distort itself into a dumbbell shape and split in two. [22] This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family. [35]

The plane of Haumea's equator is oriented nearly edge-on from Earth at present and is also slightly offset to the orbital planes of its ring and its outermost moon Hiʻiaka. Although initially assumed to be coplanar to Hiʻiaka's orbital plane by Ragozzine and Brown in 2009, their models of the collisional formation of Haumea's satellites consistently suggested Haumea's equatorial plane to be at least aligned with Hiʻiaka's orbital plane by approximately 1°. [14] This was supported with observations of a stellar occultation by Haumea in 2017, which revealed the presence of a ring approximately coincident with the plane of Hiʻiaka's orbit and Haumea's equator. [11] A mathematical analysis of the occultation data by Kondratyev and Kornoukhov in 2018 was able to constrain the relative inclination angles of Haumea's equator to the orbital planes of its ring and Hiʻiaka, which were found to be inclined 3.2° ± 1.4° and 2.0° ± 1.0° relative to Haumea's equator, respectively. They also derived two solutions for Haumea's north pole direction, pointing at the equatorial coordinates ( α , δ ) = (282.6°, –13.0°) or (282.6°, –11.8°). [16]

### Size, shape, and composition Edit

The size of a Solar System object can be deduced from its optical magnitude, its distance, and its albedo. Objects appear bright to Earth observers either because they are large or because they are highly reflective. If their reflectivity (albedo) can be ascertained, then a rough estimate can be made of their size. For most distant objects, the albedo is unknown, but Haumea is large and bright enough for its thermal emission to be measured, which has given an approximate value for its albedo and thus its size. [46] However, the calculation of its dimensions is complicated by its rapid rotation. The rotational physics of deformable bodies predicts that over as little as a hundred days, [40] a body rotating as rapidly as Haumea will have been distorted into the equilibrium form of a triaxial ellipsoid. It is thought that most of the fluctuation in Haumea's brightness is caused not by local differences in albedo but by the alternation of the side view and ends view as seen from Earth. [40]

The rotation and amplitude of Haumea's light curve were argued to place strong constraints on its composition. If Haumea were in hydrostatic equilibrium and had a low density like Pluto, with a thick mantle of ice over a small rocky core, its rapid rotation would have elongated it to a greater extent than the fluctuations in its brightness allow. Such considerations constrained its density to a range of 2.6–3.3 g/cm 3 . [47] [40] By comparison, the Moon, which is rocky, has a density of 3.3 g/cm 3 , whereas Pluto, which is typical of icy objects in the Kuiper belt, has a density of 1.86 g/cm 3 . Haumea's possible high density covered the values for silicate minerals such as olivine and pyroxene, which make up many of the rocky objects in the Solar System. This also suggested that the bulk of Haumea was rock covered with a relatively thin layer of ice. A thick ice mantle more typical of Kuiper belt objects may have been blasted off during the impact that formed the Haumean collisional family. [35]

Because Haumea has moons, the mass of the system can be calculated from their orbits using Kepler's third law. The result is 4.2 × 10 21 kg , 28% the mass of the Plutonian system and 6% that of the Moon. Nearly all of this mass is in Haumea. [14] [48] Several ellipsoid-model calculations of Haumea's dimensions have been made. The first model produced after Haumea's discovery was calculated from ground-based observations of Haumea's light curve at optical wavelengths: it provided a total length of 1,960 to 2,500 km and a visual albedo (pv) greater than 0.6. [40] The most likely shape is a triaxial ellipsoid with approximate dimensions of 2,000 × 1,500 × 1,000 km, with an albedo of 0.71. [40] Observations by the Spitzer Space Telescope give a diameter of 1,150 +250
−100 km and an albedo of 0.84 +0.1
−0.2 , from photometry at infrared wavelengths of 70 μm. [46] Subsequent light-curve analyses have suggested an equivalent circular diameter of 1,450 km. [49] In 2010 an analysis of measurements taken by Herschel Space Telescope together with the older Spitzer Telescope measurements yielded a new estimate of the equivalent diameter of Haumea—about 1300 km. [50] These independent size estimates overlap at an average geometric mean diameter of roughly 1,400 km. In 2013 the Herschel Space Telescope measured Haumea's equivalent circular diameter to be roughly 1,240 +69
−58 km . [51]

However the observations of a stellar occultation in January 2017 cast a doubt on all those conclusions. The measured shape of Haumea, while elongated as presumed before, appeared to have significantly larger dimensions – according to the data obtained from the occultation Haumea is approximately the diameter of Pluto along its longest axis and about half that at its poles. [11] The resulting density calculated from the observed shape of Haumea was about 1.8 g/cm 3 – more in line with densities of other large TNOs. This resulting shape appeared to be inconsistent with a homogenous body in hydrostatic equilibrium, [11] though Haumea appears to be one of the largest trans-Neptunian objects discovered nonetheless, [46] smaller than Eris, Pluto, similar to Makemake, and possibly Gonggong, and larger than Sedna, Quaoar, and Orcus.

A 2019 study attempted to resolve the conflicting measurements of Haumea's shape and density using numerical modeling of Haumea as a differentiated body. It found that dimensions of ≈ 2,100 × 1,680 × 1,074 km (modeling the long axis at intervals of 25 km) were a best-fit match to the observed shape of Haumea during the 2017 occultation, while also being consistent with both surface and core scalene ellipsoid shapes in hydrostatic equilibrium. [10] The revised solution for Haumea's shape implies that it has a core of approximately 1,626 × 1,446 × 940 km, with a relatively high density of ≈ 2.68 g/cm 3 , indicative of a composition largely of hydrated silicates such as kaolinite. The core is surrounded by an icy mantle that ranges in thickness from about 70 at the poles to 170 km along its longest axis, comprising up to 17% of Haumea's mass. Haumea's mean density is estimated at ≈ 2.018 g/cm 3 , with an albedo of ≈ 0.66. [10]

### Surface Edit

In 2005, the Gemini and Keck telescopes obtained spectra of Haumea which showed strong crystalline water ice features similar to the surface of Pluto's moon Charon. [17] This is peculiar, because crystalline ice forms at temperatures above 110 K, whereas Haumea's surface temperature is below 50 K, a temperature at which amorphous ice is formed. [17] In addition, the structure of crystalline ice is unstable under the constant rain of cosmic rays and energetic particles from the Sun that strike trans-Neptunian objects. [17] The timescale for the crystalline ice to revert to amorphous ice under this bombardment is on the order of ten million years, [52] yet trans-Neptunian objects have been in their present cold-temperature locations for timescales of billions of years. [37] Radiation damage should also redden and darken the surface of trans-Neptunian objects where the common surface materials of organic ices and tholin-like compounds are present, as is the case with Pluto. Therefore, the spectra and colour suggest Haumea and its family members have undergone recent resurfacing that produced fresh ice. However, no plausible resurfacing mechanism has been suggested. [19]

Haumea is as bright as snow, with an albedo in the range of 0.6–0.8, consistent with crystalline ice. [40] Other large TNOs such as Eris appear to have albedos as high or higher. [53] Best-fit modeling of the surface spectra suggested that 66% to 80% of the Haumean surface appears to be pure crystalline water ice, with one contributor to the high albedo possibly hydrogen cyanide or phyllosilicate clays. [17] Inorganic cyanide salts such as copper potassium cyanide may also be present. [17]

However, further studies of the visible and near infrared spectra suggest a homogeneous surface covered by an intimate 1:1 mixture of amorphous and crystalline ice, together with no more than 8% organics. The absence of ammonia hydrate excludes cryovolcanism and the observations confirm that the collisional event must have happened more than 100 million years ago, in agreement with the dynamic studies. [54] The absence of measurable methane in the spectra of Haumea is consistent with a warm collisional history that would have removed such volatiles, [17] in contrast to Makemake. [55]

In addition to the large fluctuations in Haumea's light curve due to the body's shape, which affect all colours equally, smaller independent colour variations seen in both visible and near-infrared wavelengths show a region on the surface that differs both in colour and in albedo. [56] [57] More specifically, a large dark red area on Haumea's bright white surface was seen in September 2009, possibly an impact feature, which indicates an area rich in minerals and organic (carbon-rich) compounds, or possibly a higher proportion of crystalline ice. [45] [58] Thus Haumea may have a mottled surface reminiscent of Pluto, if not as extreme.

A stellar occultation observed on January 21, 2017 and described in an October 2017 Nature article indicated the presence of a ring around Haumea. This represents the first ring system discovered for a TNO. [11] [59] The ring has a radius of about 2,287 km, a width of

70 km and an opacity of 0.5. It is well within Haumea's Roche limit, which would be at a radius of about 4,400 km if it were spherical (being nonspherical pushes the limit out farther). [11] The ring plane is inclined 3.2° ± 1.4° with respect to Haumea's equatorial plane and approximately coincides with the orbital plane of its larger, outer moon Hiʻiaka. [11] [60] The ring is also close to the 1:3 orbit-spin resonance with Haumea's rotation (which is at a radius of 2,285 ± 8 km from Haumea's center). The ring is estimated to contribute 5% to the total brightness of Haumea. [11]

In a study about the dynamics of ring particles published in 2019, Othon Cabo Winter and colleagues have shown that the 1:3 resonance with Haumea's rotation is dynamically unstable, but that there is a stable region in the phase space consistent with the location of Haumea's ring. This indicates that the ring particles originate on circular, periodic orbits that are close to, but not inside, the resonance. [61]

Two small satellites have been discovered orbiting Haumea, (136108) Haumea I Hiʻiaka and (136108) Haumea II Namaka. [28] Darin Ragozzine and Michael Brown discovered both in 2005, through observations of Haumea using the W. M. Keck Observatory.

Hiʻiaka, at first nicknamed "Rudolph" by the Caltech team, [62] was discovered January 26, 2005. [48] It is the outer and, at roughly 310 km in diameter, the larger and brighter of the two, and orbits Haumea in a nearly circular path every 49 days. [63] Strong absorption features at 1.5 and 2 micrometres in the infrared spectrum are consistent with nearly pure crystalline water ice covering much of the surface. [64] The unusual spectrum, along with similar absorption lines on Haumea, led Brown and colleagues to conclude that capture was an unlikely model for the system's formation, and that the Haumean moons must be fragments of Haumea itself. [37]

Namaka, the smaller, inner satellite of Haumea, was discovered on June 30, 2005, [65] and nicknamed "Blitzen". It is a tenth the mass of Hiʻiaka, orbits Haumea in 18 days in a highly elliptical, non-Keplerian orbit, and as of 2008 [update] is inclined 13° from the larger moon, which perturbs its orbit. [66] The relatively large eccentricities together with the mutual inclination of the orbits of the satellites are unexpected as they should have been damped by the tidal effects. A relatively recent passage by a 3:1 resonance with Hiʻiaka might explain the current excited orbits of the Haumean moons. [67]

At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Namaka periodically occulting Haumea. [68] Observation of such transits would provide precise information on the size and shape of Haumea and its moons, [69] as happened in the late 1980s with Pluto and Charon. [70] The tiny change in brightness of the system during these occultations will require at least a medium-aperture professional telescope for detection. [69] [71] Hiʻiaka last occulted Haumea in 1999, a few years before discovery, and will not do so again for some 130 years. [72] However, in a situation unique among regular satellites, Namaka's orbit is being greatly torqued by Hiʻiaka, which preserved the viewing angle of Namaka–Haumea transits for several more years. [66] [69] [71]

Haumea is the largest member of its collisional family, a group of astronomical objects with similar physical and orbital characteristics thought to have formed when a larger progenitor was shattered by an impact. [35] This family is the first to be identified among TNOs and includes—beside Haumea and its moons— (55636) 2002 TX 300 (≈364 km), (24835) 1995 SM 55 (≈174 km), (19308) 1996 TO 66 (≈200 km), (120178) 2003 OP 32 (≈230 km), and (145453) 2005 RR 43 (≈252 km). [3] Brown and colleagues proposed that the family were a direct product of the impact that removed Haumea's ice mantle, [35] but a second proposal suggests a more complicated origin: that the material ejected in the initial collision instead coalesced into a large moon of Haumea, which was later shattered in a second collision, dispersing its shards outwards. [74] This second scenario appears to produce a dispersion of velocities for the fragments that is more closely matched to the measured velocity dispersion of the family members. [74]

The presence of the collisional family could imply that Haumea and its "offspring" might have originated in the scattered disc. In today's sparsely populated Kuiper belt, the chance of such a collision occurring over the age of the Solar System is less than 0.1 percent. [75] The family could not have formed in the denser primordial Kuiper belt because such a close-knit group would have been disrupted by Neptune's migration into the belt—the believed cause of the belt's current low density. [75] Therefore, it appears likely that the dynamic scattered disc region, in which the possibility of such a collision is far higher, is the place of origin for the object that generated Haumea and its kin. [75]

Because it would have taken at least a billion years for the group to have diffused as far as it has, the collision which created the Haumea family is believed to have occurred very early in the Solar System's history. [3]

Joel Poncy and colleagues calculated that a flyby mission to Haumea could take 14.25 years using a gravity assist at Jupiter, based on a launch date of 25 September 2025. Haumea would be 48.18 AU from the Sun when the spacecraft arrives. A flight time of 16.45 years can be achieved with launch dates on 1 November 2026, 23 September 2037 and 29 October 2038. [76] Haumea could become a target for an exploration mission, [77] and an example of this work is a preliminary study on a probe to Haumea and its moons (at 35–51 AU). [78] Probe mass, power source, and propulsion systems are key technology areas for this type of mission. [77]

## A cosmic alignment

Scientists had the chance to learn more about this space oddity when Haumea passed in front of the star URAT1 533-182543 on Jan. 21, 2017. Although objects pass in front of stars quite often, it's difficult to accurately predict the specific time and location of these events, study co-author Pablo Santos Sanz told Space.com. Santos Sanz is an astrophysicist at the Instituto de Astrofísica de Andalucía in Granada, Spain.

Santos Sanz's team coordinated 12 telescopes, from 10 different labs, to observe starlight blocked by Haumea and thus better determine its size and shape. Normally, shadows are larger than the objects that cast them. For instance, you can move your hand closer and farther from a flashlight to make its shadow grow and shrink. But the star was so far from Earth relative to Haumea that it projected the dwarf planet's shadow at full size.

"This is a very powerful technique &hellip to obtain sizes," Santos Sanz said. The researchers discovered that Haumea's longest axis is at least 1,430 miles (2,300 kilometers) across &mdash 17 percent larger than previous estimates.

The more accurate measurements of Haumea enabled the astronomers to calculate many of the dwarf planet's other properties. Factoring in the rotation gave them its 3D shape and volume. Combining this with its mass &mdash derived from the orbits of its moons &mdash yielded Haumea's density. It was lower than previous estimates, Santos Sans said, but was closer to that of other Kuiper Belt objects, like Pluto.

But these new measurements may cost Haumea its dwarf-planet status. Although many planets and dwarf planets are not perfect spheres &mdash Earth, for instance, bulges a bit at the equator &mdash they are all large enough to have become round due to their own gravity. In contrast, most smaller objects don't have enough gravity to overcome their own rigidity, so they end up oddly shaped or lumpy. This criterion is central to the contentious definition of a dwarf planet, and the more accurate picture of Haumea that emerged from the study appears not to meet it.

"I don't know if this will change the definition [of a dwarf planet]," Santos Sanz said. "I think probably yes, but probably it will take time."

Most surprisingly, the scientists learned that Haumea has rings.

The night Haumea crossed in front of the distant star, Santos Sanz and team leader José Luis Ortiz, also of the Instituto de Astrofísica de Andalucía, looked at the new data.

"We started to see something weird in the light curve," Santos Sanz said. The light dimmed just before and after Haumea passed in front of the star, as if something else were obscuring it. "I remember that José Luis, from the first [moments], said, 'OK, this could be a ring,'" Santos Sanz said. Months of scrutiny bore out the scientists' initial suspicions: The results suggest that Haumea's equator is encircled by a 43-mile-wide (70 km) ring of debris located about 620 miles (1,000 km) from the dwarf planet's surface.

"Rings are usually the sign of a collision that happened not too long ago," Yale astronomer David Rabinowitz, who is unaffiliated with the study, told Space.com. For Rabinowitz, this means sometime between several hundred-million years ago and one billion years ago. The search for the rings' origin makes the system that much more interesting, he added. It's another mystery about the dwarf planet begging for an answer.

## Mike Brown's Planets

A thoroughly sporadic column from astronomer Mike Brown on space and science, planets and dwarf planets, the sun, the moon, the stars, and the joys and frustrations of search, discovery, and life. With a family in tow. Or towing. Or perhaps in mutual orbit.

### Haumea

Haumea I, Hi'iaka, discovered 2005 Jan 26 by M.E. Brown, A.H. Bouchez, and the Keck Observatory Adaptive Optics team

Hi'iaka was born from the mouth of Haumea and carried by her sister Pele in egg form from their distant home to Hawaii. She danced the first Hula on the shores of Puna and is the patron goddess of the island of Hawaii and of hula dancers.

Haumea II, Namaka, discovered 2005 Nov 7 by M.E. Brown, A.H. Bouchez, and the Keck Observatory Adaptive Optics teams

Namaka is a water spirit in Hawaiian mythology. She was born from the body of Haumea and is the sister of Pele. When Pele sends her burning lava into the sea, Namaka cools the lava to become new land.

Finally - all the dwarf planets are accepted as such and have been awarded real names!

And yet confusion persists: the USGS list records "Sierra Nevada Observatory, Spain" as the discovery location of Haumea .

I think that is the part that will have to wait for posterity to decide.

did you name the moons . you found them.

What name did the Spanish team propose?

I was told that the Spanish team proposed an Andalusian variant of Persephone, though I can't figure out exactly what that is.

According to the Planetary Society (http://www.planetary.org/blog/) blog the Spanish group proposed Ataecina, an Iberian goddess.

"Back when I thought that maybe the IAU was going to vote that anything the size of Pluto or larger was a planet I was going to argue that Santa was indeed a planet – as long as you looked at it at exactly the right angle (luckily, the IAU was much more sensible, so I did not have to make such a crazy argument)."

No, wrong again: the IAU was not much more sensible but much less so. If this object is a dwarf planet, then it is a planet. I'm assuming that in giving it dwarf planet status, the IAU has confirmed it is in hydrostatic equilibrium. If you're looking for posterity to decide, it's much more important that the definition stating that dwarf planets are not planets at all be overturned than that we find out who discovered EL61 first. The former is a question regarding the nature of this object the latter is nothing more than a battle of egos.

An object in hydrostatic equilibrium orbiting a star is a planet. Sorry, but you will have to make this argument for EL61 after all, whether now or in 2015.

Laurel: "that we find out who discovered EL61 first. is nothing more than a battle of egos."

Easy for you to say. Imagine spending hours and hours studying the sky and then finding an object. And then spending months calculating the object's orbit an properties to confirm what you found, only to have it scooped by someone spying on your observations.

Imagine Clyde Tombaugh spending much of his life studying photographic plates to eventually find Pluto. So if a janitor at Lowell looked over his shoulder and ran to the papers saying that he found the 9th planet, any protest by Tombaugh would be his "ego" talking?

Laurel:
You might be surprised to learn that I would be perfectly happy if you called dwarf planets "planets." But, of course, I am also perfectly happy if you do not. As I have written in detail, the science is all in the classification. The 8 planets are significantly different than the many many dwarf planets. Once that distinction is made, I don't care what you call them. We could call the 8 big things "grogs" and the other 50 round things "bloogs" and it would not matter to me. Classification is science. The rest is culture. I make no claim to know what it is best for culture to do.

I do have to object, though, to your contention that the naming rights are only about egos. I actually think that in this case it matters to take a stand against what appears to have been [to me, at least. you are welcome to a different opinion] scientific fraud.

If we scientists allow fraud to occur with no sort of sanction we have lost any authority that science confers. This matters. This matters alot.

It occurs to me that since your group discovered the two moons, you would presumably have had naming rights. Since it would be pretty weird to have a dwarf planet named after an Andalusian goddess with two "Hawaiian" moons, I can see why the IAU would have opted for your name for the planet as well, whether they believed you made the discovery or not.

In fact, I kind of suspected something like this would happen, sooner rather than years from now after much wrangling.

So do we know what is planned for getting the other TNOs categoried as dwarf planets? Will Sedna, Quaoar, Orcus and Ixion be classified as dwarf planets soon?

I think the IAU (and even Mike Brown) are making a logical assumption that Haumea is in hydrostatic equilibrium. Since this plutoid has known moons, the mass can be more accurately determined (though size and thus density are more of a best guess). With the fast rotation rate, the less dense it is, the more distorted it will be. Given Haumea's weird shape, if Haumea did not have any known moons, (and thus would have a very unknown mass), I am not sure if the IAU (or Mike) would have given Haumea plutoid status this quickly. The Kuiper Belt is still a very unknown region of the solar system. We still have yet to demonstrate the compositional difference between a comet nucleus like Hale-Bopp (40km in diameter), a centaur like Chariklo (258km in diameter), and a plutoid like Eris.
-- Kevin Heider

Mike, I'm happy to hear that you would be comfortable with categorizing dwarf planets as a subclass of planets. The classification scheme that would keep the term planet broad to refer to any object in hydrostatic equilibrium orbiting a star does in fact make room for distinguishing objects based on various factors including dynamics. So dwarf planets are planets but small ones that are not gravitationally dominant. This is far better than the IAU definition you describe as "sensible" because that one ignores what objects are and classifies them solely by where they are.

Having thought about the naming rights issue, I agree that it is not just about ego. However, if you have a problem with scientific fraud, then you should not be so willing to accept the IAU decision, which was made in violation of the IAU's bylaws (resolutions are supposed to be vetted by a committee in advance, not introduced in real time) by only four percent of its members through what was essentially a hijacking of the vote by dynamicists revolting against the original definition the IAU's own committee proposed.

As far as posterity, I'm the same age as you, and I plan to be around to see this IAU travesty undone. Maybe that means I'll see the naming rights controversy about Haumea resolved as well.

Laurel: I'm glad you came around about the naming rights issue. And I agree the IAU should have determined its decision on the proponderance of the evidence and officially awarded the discovery to Mike Brown. The compromise should have been simply not sanctioning the Spanish team, which they should.

It's been 10 more years, any updates at all on this controversy?

The arguments over priority and naming put Haumea in good company: that of Neptune. Your naming got settled faster, at least.

Do we have any more observations, orbital data, or occultation data on Namaka?
-- Kevin Heider

Kevin:
Namaka is, of course, the moon that I wrote all about back in the spring when searching for moon shadows (see here.

In the past few months we have gotten a better orbital solution and we think the occultations might occur for a few more years (!). We will try again in the spring to see what we can see!

Finally, finally, finally! Here's to license plate numbers! May they serve their purpose more quickly in the future. Congratulations Mike, I think the name is wonderful and clever.

I don't mean to change the subject, but speaking of dwarf planets without names, I have been wondering about 2002 AW197. I notice that of all the large objects you have discovered, you don't have a page on your website about this one. Is there a reason why? I have not heard too much about it since it could be one of the next candidates to be named.

The astrology community thanks you for something positive to work with. Joy.

I'm still waiting for Lilah though!

A question: since there are other KBOs thought to have originated from Haumea after a massive collision, will these now be given Hawaiian names as well? I suppose they'd be like children who left home.

the goal is to name them specifically after other children of Haumea, though we will eventually run out!

Finally - I am glad that the Hawaiian name was chosen, I like it. Congratulations, Mike.

This decision makes now 2002 TC302 presumably the largest known Kuiper Belt object without a name, isn't it? But till a sixth dwarf planet can be proclaimed we will probably have to wait several years, until hard evidence about the equilibrium of candidates is found. I mean, unless somebody (you?) comes forward with new surprises in the order of M < 1 . -)

I'm a bit surprised that this object received dwarf planet designation due to its odd shape. How can we be sure it is in hydrostatic equilibrium? Being in a state of hydrostatic equilibrium is a requirement for an object to be designated a dwarf planet. Was this designation premature?

Without space missions it is almost impossible to certify 100% the hydrostatic equilibrium but one can get a fair assessment from size and mass.
The uncertainties on size for most candidates to dwarfplanethood remain huge though. It would be great if more star occultations could be studied (like the occultation by Pluto Mike Brown has participated to - see "Occult Sciences" on this blog). For Varuna-sized or 2004XR190-sized objects, astrometry will be crucial though to be able to predict where the occultation spot will pass on Earth.
Perhaps when astrometry improves (e.g. with Gaia mission), astronomers/planetologists may carry out more star campaigns occultation on 500-1000km sized objects.

Hi, do you remember what time it was on Dec 28 2004 when you discovered Haumea?

Speaking of elongated spheroids what is the latest word on Varuna (Source: Jewitt and Sheppard 2002)? Any reason to still suspect that it is also a triaxial ellipsoid with a rapid rotation peroid? Or is it more likely to be a contact binary due to the smaller size?
-- Kevin Heider

Mike, why the IAU-CSBN don't choose a neutral name for 2003EL61 neither Ataecina nor Haumea?

Many congrats on your latest discovery!

I am an astrophotographer based in Athens, Greece and I would like to image our fifth dwarf planet. However, I have been unsuccessful in locating the J2000 coordinates for Haumea.

Are the coordinates for Haumea now public record or are they still classified? If the former, I would be grateful a lead in this regard.

Thank you and congrats once again!

Anthony Ayiomamitis
Athens, Greece
(http://www.perseus.gr)

The ephemeris service at JPL was very helpful. I will send email when I have results.

I had proposed a neutral name for Haumea but it wasn't used. I never turned a telescope on the object. But I did use GravitySimulator on it. I believe it's the lost moon of Triton so I proposed the name "Rhode", who in Greek mythology was the sister of Triton and the godess of the Island of Rhodes (think "The Colosus of Rhodes). This was ignored, of course, but that's OK. I cheerfully accept the name Haumea (actually it's pretty good)and gleefully accept the plutoing of Pluto. I think Pluto, Triton, Haumea, and Eris aren't planets, they belong in an even more elite club - surviving Lagrangoids formed in an L4 or L5 point.

I have thought for some time that Triton must have had a lost moon or it could not be captured into it's backwards orbit around Neptune. I set up simulations with binaries consisting of two Triton masses orbiting at various distances (12,000 - 50,000 km)flying past Neptune at a distance similar to Triton's orbit today (it was kind of hard to aim. Sometimes one would be captured. It would do this by transferring momentum to the other member of the pair which would then be propelled away a gravity slingshot. This is capable of propelling the departing object about as far as (sometimes more than) the distance of Eris. At that point I thought maybe Eris was the lost moon of Triton.

After a few simulations, there was only one object after the flyby. I said, "where is the other one?" But checking the mass of the object showed it was twice the mass of Triton. By that time I was beginning to learn the simulator. Practice makes perfect in everything. I set up a standardized start for the simulations and saved it. But I added a few kilometers separation between the two simulated Tritons.

Observation had showed me what to look for, and that was the angle formed by the centers of mass of Neptune and the two Tritons at closest approach. If at that point they form a straight line, you get maximum launch velocity for the escaping object. However, if the three objects form a right angle, in other words one Triton follows behind the other, then apparently Neptune cancels their rotation with repect to each other. There is no centrifugal force to counter the two Tritons' gravitational pull and they collide.

By this time I had noticed the similarites in the four objects. Pluto and Eris are the same size. Triton is the mass of Pluto plus the combined mass of Uranus's major moons. Haumea has apparently been stripped of it's ices. It is a little smaller than the stripped core of Pluto so apparently it might have lost some stone, too. The "Iron Dwarf". I like it!

I got scooped on this by Craig Agnor and Douglas Hamilton, who got the simulations done and published in a peer reviewed journal and get credit for the idea. I was expecting this and congradulate Agnor and Hamilton on a job well done. They did postulate a moon kind of like Charon to carry away the excess angular momentum to get into orbit and I wasn't able to get around to how large the mass must be to effect capture, I simply assumed that binaries formed in the Sun/Neptune Lagrange points L4 and L5.

Mike, you should take a good humor at getting scooped. Now, Ortiz's discovery photo undeniably exists. Marsden published a how-to for comet hunters in Sky & Telescope several years ago and he said that the first thing you were supposed to do is see if it has been discovered by somebody else. Ortiz just got a little creative, that's all. If he wanted to look at your logs, how would he know to do that unless he had discovered it himself? He might have thought it was a nova or something when he first looked at it and put it aside when he couldn't find it again. Somewhere in the back of his mind is, "look for news from that part of the sky". All this is a legitimate part of the discovery process.

Incidentally, I looked at Ortiz's observing logs. He was at the telescope that night, making a "calibration run".

The rules for discovery credit were set up for amateur astronomers, since historically it is they who have discovered the most comets. Comet hunting is a horserace to see who gets a coherent report in first. Most comets have two names. They decided not to do that with Plutoids. But they must put, for posterity, tha name of the winner of the horserace, and that was Ortiz.

## Watch the video: Haumea - The Egg Shaped World Beyond Pluto Episode 1 4K UHD (July 2022).

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