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EPIC 201367065?

EPIC 201367065?


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I was extremely stoked when I read an article in January of this year that the Kepler2 mission found three Earth-sized objects (one possibly in the habitable zone) transiting a star only 150LY away. I haven't heard anything since, not even if this star and planets (confirmed) have been given a Kepler designation. I guess I would like to know if JWST or some other upcoming mission will be able to give us more info on this system. I can't imagine how excited I will be if TESS gives us something even closer!!


Beichman et al. (2016) used the Spitzer Space Telescope to view two systems, EPIC 202083828 (one planet) and the aforementioned EPIC 201367065 (three planets), also known as K2-3. The authors describe several ways in which the observations by Spitzer complement the Kepler data:

  • Spitzer has better sampling while maintaining the same signal-to-noise ratio, constraining various orbital parameters even more.
  • Observations by Spitzer occurred over twelve months after the Kepler observations, allowing for more detailed information on the position and orbits of the planets over time.
  • Limb darkening is less of an issue in Spitzer's observations than it was in Kepler's data.
  • Spitzer can reject false transit positives by looking at how the transit depth changes over different wavelengths.
  • There is less noise from the stellar photosphere in infrared bands.

All of this led to much lower uncertainties in parameter observations in Spitzer's data alone; combined with Kepler's observations, the uncertainties were reduced even further. Period estimates and transit depths, for instance, saw significant improvement.

Finally, the authors recommend that the system be observed by the James Webb Space Telescope. That won't be launched for another two years, but I suspect its versatility over various wavelengths will better constrain data from EPIC 201367065 and other systems.

Crossfield et al. (2015) say that the James Webb Space Telescope has the capability to detect spectral signs in the atmospheres of the planets, based on certain models (Hubble could also observe them). I don't think JWST has been assigned specific targets that include this system, but that's just a guess.

In the case of the first system measured by Beichman et al., EPIC 202083828, ground-based telescopes could also give more information about spectroscopy to rival JWST, according to Schlieder et al. (2016). Perhaps EPIC 201367065 could also be observed by these telescopes.


Potentially habitable super-Earth K2-3d observed transiting parent star

An artist’s impression of a super-Earth like K2-3d orbiting a red dwarf star. Image credit: NASA. A group of researchers from the National Astronomical Observatory of Japan (NAOJ), the University of Tokyo, and the Astrobiology Center among others has observed the transit of a potentially Earth-like extrasolar planet known as K2-3d using the MuSCAT instrument on the Okayama Astrophysical Observatory 188-centimetre telescope. A transit is a phenomenon in which a planet passes in front of its parent star, blocking a small amount of light from the star, like a shadow of the planet. While transits have previously been observed for thousands of other extrasolar planets, K2-3d is important because there is a possibility that it might harbour extraterrestrial life.

By observing its transit precisely using the next generation of telescopes, such as the Thirty Metre Telescope (TMT), scientists expect to be able to search the atmosphere of the planet for molecules related to life, such as oxygen.

With only the previous space telescope observations, however, researchers can’t calculate the orbital period of the planet precisely, which makes predicting the exact times of future transits more difficult. This research group has succeeded in measuring the orbital period of the planet with a high precision of about 18 seconds. This greatly improved the forecast accuracy for future transit times. So now researchers will know exactly when to watch for the transits using the next generation of telescopes. This research result is an important step towards the search for extraterrestrial life in the future.

K2-3d
K2-3d is an extrasolar planet 147 light-years away that was discovered by NASA’s Kepler K2 mission. K2-3d’s size is 1.5 times that of the Earth. The planet orbits its host star &mdash also known as EPIC 201367065, hosting two other super-Earth exoplanets, K2-3b and c &mdash which is half the size of the Sun, with a period of about 45 days. Compared to the Earth, the planet orbits close to its host star (about &frac15 of the Earth-Sun distance). But, because the temperature of the host star is lower than that of the Sun, calculations show that this is the right distance for the planet to have a relatively warm climate like the Earth’s. There is a possibility that liquid water could exist on the surface of the planet, raising the tantalising possibility of extraterrestrial life. This collage summarises the research. Using the Okayama 188-centimetre Reflector Telescope and the observational instrument MuSCAT (bottom left), researchers succeeded in observing the extrasolar planet K2-3d, which is about the same size and temperature as the Earth, pass in front of its parent star blocking some of the star’s light (artistic visualisation at the top), making it appear to dim (real data on the bottom right). Illustration credit: NAOJ. K2-3d’s orbit is aligned so that as seen from Earth, it transits (passes in front of) its host star. This causes, short, periodic decreases in the star’s brightness, as the planet blocks some of the star’s light. This alignment enables researchers to probe the atmospheric composition of these planets by precise measurement of the amount of blocked starlight at different wavelengths.

About 30 potentially habitable planets that also have transiting orbits were discovered by NASA’s Kepler mission, but most of these planets orbit fainter, more distant stars. Because it is closer to Earth and its host star is brighter, K2-3d is a more interesting candidate for detailed follow-up studies. The brightness decrease of the host star caused by the transit of K2-3d is small, only 0.07 percent. However, it is expected that the next generation of large telescopes will be able to measure how this brightness decrease varies with wavelength, enabling investigations of the composition of the planet’s atmosphere. If extraterrestrial life exists on K2-3d, scientists hope to be able to detect molecules related to it, such as oxygen, in the atmosphere.

MuSCAT observations and transit ephemeris improvements
The orbital period of K2-3d is about 45 days. Since the K2 mission’s survey period is only 80 days for each area of sky, researchers could only measure two transits in the K2 data. This isn’t sufficient to measure the planet’s orbital period precisely, so when researchers attempt to predict the times of future transits, creating something called a “transit ephemeris,” but there are uncertainties in the predicted times. These uncertainties grow larger as they try to predict further into the future. Therefore, early additional transit observations and adjustments to the ephemeris were required before researchers lost track of the transit. Because of the importance of K2-3d, NASA’s Spitzer Space Telescope observed two transits soon after the planet’s discovery, bringing the total to four transit measurements. However, the addition of even a single transit measurement farther in the future can help to yield a significantly improved ephemeris.

Using the Okayama 188-centimetre Reflector Telescope and the latest observational instrument MuSCAT, the team observed a transit of K2-3d for the first time with a ground-based telescope. Though a 0.07 percent brightness decrease is near the limit of what can be observed with ground-based telescopes, MuSCAT’s ability to observe three wavelength bands simultaneously enhanced its ability to detect the transit. By reanalysing the data from K2 and Spitzer in combination with this new observation, researchers have greatly improved the precision of the ephemeris, determining the orbital period of the planet to within about 18 seconds (1/30 of the original uncertainty). This improved transit ephemeris ensures that when the next generation of large telescopes come online, they will know exactly when to watch for transits. Thus these research results help pave the way for future extraterrestrial life surveys.

Future work
NASA’s K2 mission will continue until at least February 2018 and is expected to discover more potentially habitable planets like K2-3d. Furthermore, K2’s successor, the Transiting Exoplanet Survey Satellite (TESS), will be launched in December 2017. TESS will survey the whole sky for two years and is expected to detect hundreds of small planets like K2-3d near our solar system. To characterise a ‘second Earth’ using the next generation of large telescopes, it will be important to measure the ephemerides and characteristics of planets with additional transit observations using medium sized ground-based telescopes. The team will continue using MuSCAT for research related to the future search for extraterrestrial life.


Astrophysics Ph.D. Student Discovers New Solar System

Bay-Area native Erik Petigura, a 5 th year doctoral student in Astrophysics, became interested in astronomy at five years old when he watched Carl Sagan’s T.V. series, Cosmos. As an undergrad at Berkeley, he double-majored in Physics and Astrophysics, with the goal of gaining a better understanding of the planets outside of our system. In January, Petigura made the remarkable discovery of a new solar system with one planet that is very similar to our own.

By analyzing data from NASA’s Kepler Space Telescope, Petigura identified three planets that orbit the star Epic 201367065 — which is half the size of the Sun. The outer-most planet in the system is just slightly bigger than the size of the Earth and receives only 40% more sunlight.

“This is one of the most Earth-like planets known to date,” Petigura says. “It means that the potential for atmospheric chemistry and perhaps even life on this planet is very interesting and worth following up on,” he adds.

The discovery came about from what Petigura describes as “an interesting twist of fate,” after Kepler experienced a hardware failure about a year ago. Previously, the telescope was intended to study one part of the sky for seven years, But after it malfunctioned, NASA created a new survey called K2. The new mission inspects more sky in a shorter period of time, which yields a greater discovery of nearby planets.

Although Kepler has found over 4,000 planets, most of them have been about 1,000 light years away. In contrast, the planets in the recently discovered system “are only 100 light years away, so they’re 10 times closer than the typical star that Kepler found planets around in the original mission,” Petigura explains. Because the system is so close, it will be easy to continue to observe. Over the next few months, researchers will learn both the mass and size, which will allow them to calculate the density. This will help scientists determine if the planet is rocky like the Earth or gaseous like Neptune.

Petigura is involved in the efforts to measure both the masses of the planets and what elements compose their atmospheres. “I think those two observations are going to bear directly on our understanding of how unique our own Earth is,” Petigura says. Soon, researchers will also be observing the planets with the Hubble Space Telescope.

In his research, he has determined that 74% of Sun-like stars have at least one orbiting planet. To Petigura, the discovery of the new system proves that Kepler has the potential to reveal incredible findings.

About Melissa Hellmann

Melissa Hellmann is a second-year student at UC Berkeley's Graduate School of Journalism where she's focusing on long-form writing. When she's not writing for GradNews, she enjoys reporting on Asia and human rights issues.


Back Alley Astronomy

Eleven days ago, just in time for Twelfth Night, a research team led by Guillermo Torres reported the “Validation of Twelve Small Kepler Transiting Planets in the Habitable Zone.” The cybermedia loved the story, broadcasting many thrilling variations on the theme of Most Earthlike Planet Yet! Now that the piping pipers and dancing ladies have come and gone, I’ve found time to look behind the barrage of news items and unwrap these Gifts of the Magi.

In fact, Torres and colleagues have brought us only two new Earth-like objects (though some popular accounts suggested other numbers, ranging from one to eight to a thousand). Their official names are Kepler-438b and Kepler-442b. Torres’ collaborators, most of whom are associated with the Kepler Mission, started their search for another Earth 2 about a year ago. This was some time after the announcement of Kepler-62f, the first plausibly terrestrial planet orbiting in an extrasolar habitable zone. They began by selecting all Kepler candidates then believed to be in the habitable zone and smaller than 2.5 Earth radii (2.5 Rea). Then they conducted extensive follow-up observations and analyses to derive the most robust parameters possible for each object of interest.

In the end Torres and colleagues were able to validate a dozen of these smallish planets, though the status of the twelfth is less secure than the others. Meanwhile, a subgroup of his collaborators reported one of the most Earth-like candidates (Kepler-186f) separately from the rest. Then another of those candidates (Kepler-296f) was found to orbit a member of a close binary system, making the planet’s characterization more difficult. Of the remainder, three are clearly larger than 2 Rea, ruling out a terrestrial composition, and only two are smaller than 1.5 Rea, widely regarded as the approximate upper boundary for Earth-like composition. Those two objects were at the center of last week’s hoopla.

Along with Kepler-62f and Kepler-186f, we now have four robust candidates for terrestrial composition and surface water. And yes, the new ones, especially Kepler-438b, compare very favorably with the earlier candidates, as shown in Table 1:

If each of these objects had the same iron/silicate composition as Earth, their respective masses would be about 1.5, 1.6, 2.5, and 3.5 Mea (Zeng & Sasselov 2013, Lissauer et al. 2013). Although there is probably an upper mass limit for the habitability of a purely rocky planet, based on the reduced likelihood of plate tectonics at high mass, no consensus has emerged on what the limit might be. My conservative guess is about 3 Mea, disfavoring Kepler-62f.

A somewhat wetter composition – approximately 10% ice, 90% iron/silicate – would reduce the two smaller objects to about 1 Mea and the two larger to about 2 Mea. Such a large watery component, however, would most likely render all these planets uninhabitable, because surface water would be isolated from core metals by an ice layer, and thus would lack the chemical diversity believed necessary for the emergence of life (Alibert 2014).

Regarding planetary climates, the table above presents the equilibrium temperatures (Teq) estimated by Kepler Mission scientists. All planets except Kepler-186f have Teq within the traditional limits (i.e., 185-303 K Kopparapu et al. 2013). These limits are based on the fact that Earth, with its Teq of 255 K and mean surface temperature of 288 K, is securely parked in a habitable space. However, many studies over the past few years have debated the definition of the habitable zone (e.g., Zsom et al. 2013) as well as the use of Teq in this definition (e.g., Kastings et al. 2014). Some astronomers have argued for extending the habitable zone’s inner limits (Seager 2013), while others have argued against it (Kastings et al. 2014). Amid these debates, all four planets remain promising, even Kepler-186f. Its mass predicts a substantial atmosphere whose greenhouse effect could raise surface temperatures appropriately.

Another key factor in understanding surface conditions on an extrasolar planet is rotation. Three out of four planets in Table 1 orbit within their host star’s tidal locking radius (Selsis et al. 2007). Therefore, their rotation is likely to be “synchronous” with their orbits – in other words, they always turn the same hemisphere toward their suns. A possible outcome of synchronous rotation is loss of atmosphere through freeze-out of volatiles on the permanent night side, rendering the planet uninhabitable. Fortunately, studies old and new (Joshi 2003, Yang et al. 2014) provide scenarios that avoid this outcome.

As Yang and colleagues recently argued, the major variables involved are the synchronous planet’s complement of surface water, its geothermal flux (i.e., volcanism and related processes), and the percentage of its night side covered by land. On an ocean world where geothermal flux is strong and scattered archipelagos are the only land, some sea ice would accumulate on the night side, but liquid water would be abundant everywhere. On a world with oceans, continents, and geothermal flux in the range of Earth values, ice sheets would accumulate on night-side continents, but total freeze-out would not occur and clement conditions would prevail. Only a world with low geothermal flux, limited surface water, and a night side covered by continents would build massive ice sheets and suffer complete loss of liquid water. Thus the odds of a tidally locked planet with livable surface conditions seem favorable.

So far, so good. At least three out of four planets remain plausible candidates for the evolution and survival of life, and the two newest arrivals appear very similar to the old ones. However, Kepler-438b and -442b differ from Kepler-62f and -186f in one important way: each of the new candidates is the only detected planet orbiting its host star. Indeed, their loneliness made it more difficult for Torres’ team to validate them, since validation gets progressively easier as the number of transiting candidates per star increases.

I found this detail surprising and a little disappointing. Each of the older candidates is the outermost planet of five, and in both systems, all orbits are mutually well-aligned and all planets are smaller than 2 Rea. These data tell us that the systems had relatively placid dynamic histories, and that their planets are likely to be rich in refractory elements. They are also consistent with our expectation that planets in the range of 1 to 6 Rea occur in compact systems with neighboring planets of similar size.

So what’s going on with Kepler-438 and Kepler-442? Does each star host only one planet within 0.5 AU? Or does each actually host numerous small planets, except that the Earth-like candidates happen to be significantly misaligned with the rest?

As far as I understand, it’s possible for a planetary system to be “flat” (i.e., co-planar with minimal misalignment), yet our viewing angle can be such that only the inner planets are visible in transit, while the outer planets remain just outside of range. Regardless of viewing angle, however, if an outer planet transits, then mutually aligned inner planets should also transit. At face value, then, Kepler-438b and Kepler-442b do not seem to be members of the compact multiplanet systems we’ve come to know and love. I look forward to future investigations on this point.

Debates aside, all four of these candidates still look promising. Their charms were enhanced by a cover story in Scientific American that appeared on the newsstands when Torres et al. announced their findings: “The Hunt for Planets Better Than Earth.” Written by Rene Heller, this article presents a plain-language summary of Heller & Armstrong’s 2014 study of “Superhabitable Planets” in Astrobiology.

Heller starts by noting that Earth is hardly the “best of all possible worlds,” because its host star will eventually evolve off the main sequence and evaporate all our water. (Only 1.75 billion years to go!) If we want a longer-lived biosphere, we need to find planets that orbit M and K dwarfs, since these types will continue burning on the main sequence for many tens of billions of years. Recognizing that M dwarfs are subject to “powerful stellar flares and other dangerous effects,” Heller singles out K dwarfs in particular as occupants of the “sweet spot of stellar superhabitability.” In addition, he argues that planets more massive than Earth – ideally about 2 Mea – are friendlier to life than planets in the mass range of Venus and Earth. This is because more massive planets will probably have higher levels of geothermal flux, which sustains the carbon cycle and maintains the planetary magnetic field, thereby averting both a CO2 greenhouse and atmospheric erosion by cosmic rays over multi-billion year time scales.

All the Kepler planets summarized on this page are approximately consistent with Heller’s criteria, although none provide a perfect fit: The only candidate orbiting a K dwarf is Kepler-62f, which must be about 3.5 Mea if it is purely rocky.

the problem with M dwarfs

The three best Goldilocks candidates, including the two newest, orbit M dwarfs. These relatively dim stars have masses between about 10% and 60% Solar (0.1-0.6 Msol). They represent the commonest spectral type in the Galaxy, accounting for 75% of the overall stellar population. They also seem to be rich in small planets, and their habitable zones have much smaller radii than the ones around more massive stars. These criteria mean that habitable planets around M dwarfs have much shorter orbital periods than those around Sun-like stars. Shorter periods, in turn, mean that habitable M dwarf planets are more likely to transit than habitable G dwarf planets, and are easier to detect when they do.

All these circumstances help to explain the fact that, even though Kepler was specifically designed to study Sun-like stars (spectral types G, early K, and late F), only one of the four candidates discussed here (Kepler-62f) has a reasonably Sun-like host.

Yet M dwarfs still have problems. A brand-new study by Luger & Barnes (2015) provides a convenient rundown:

  • M dwarfs typically emit much of their luminosity in X-rays and extreme ultraviolet wavelengths, which can drive atmospheric escape and harm organisms.
  • They are subject to brief flaring events in which they emit a much higher energy flux, which can destroy volatiles and erode atmospheres, especially in planets orbiting in their close-in habitable zones.
  • They spend a long stretch of their formative years at luminosities one to two orders of magnitude higher than they will be after they settle down on the main sequence. Since planetary systems must form during this epoch, gestating M dwarf planets might develop a runaway greenhouse early on and lose all their volatiles.
  • This luminosity evolution also means that the planets we now observe in M dwarf habitable zones probably formed when habitable temperatures were available only at much wider separations from the central star. Such planets would be born bone-dry.

We can expect to hear about many more small planets orbiting M dwarfs over the next few years. In fact, the successor mission to Kepler, known as K2, has just reported a system of three planets orbiting an M0 star located only about 45 parsecs (147 light years) away, much closer than any of the planets in Table 1 (Crossfield et al. 2015). The host star was evidently missed by the major catalogs of nearby stars (Henry Draper, Gliese, and Hipparcos). As a result, instead of a familiar HD, GJ, or HR designation, it is known by one of the most unmemorable character strings I’ve ever seen: EPIC 201367065. The planets, which received the usual unglamorous designations b, c, and d, have respective radii of 2.14, 1.72, and 1.52 Rea, and respective orbital periods of 10, 25, and 45 days.

EPIC 201367065 System Architecture

Depending on one’s definition of the habitable zone, planet d is located either just inside the inner edge (Zsom et al. 2013), indicating potential surface water if certain finely tuned conditions are met, or significantly starward of the inner edge (Kasting et al. 2014), implying temperatures far too high for liquid water. In addition, within error margins, this planet’s radius might be as small as 1.32 Rea, putting it in the same ballpark as Kepler-442b. As the authors note, “this planet [is] a very interesting potential super-Venus or super-Earth.” Cheers and applause all around!

I’d been worrying that K2 would find only boring old Hot Jupiters, so this early return is a very pleasant surprise . . . even if it compounds the problem of too many interesting planets orbiting the wrong kind of star.

Nonetheless, I'm still a bit troubled that after more than three years of data collection by Kepler, and more than a year of additional analyses, we have only one oversized candidate for the status of terrestrial planet in the habitable zone of a K or G star. Are they intrinsically rare, or just hard to find?


EPIC 201367065? - Astronomy

NASA's Kepler Space Telescope has been hobbled by the loss of critical guidance systems but can still find good stuff - most recently a star with three planets only slightly larger than Earth, one in the "Goldilocks" zone, a region where surface temperatures could be moderate enough for liquid water and therefore perhaps life as we know it, to exist.

EPIC 201367065, is a cool red M-dwarf star about half the size and mass of our own sun. It is 150 light years, making it among the top 10 nearest stars known to have transiting planets. The star's proximity means it's bright enough for astronomers to study the planets' atmospheres to determine whether they are like Earth's atmosphere and possibly conducive to life.

"A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many exoplanets discovered by the Kepler mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it," said Ian Crossfield, the University of Arizona astronomer who led the study.


arXiv:1501.03798

The three planets are 2.1, 1.7 and 1.5 times the size of Earth. The smallest and outermost planet, at 1.5 Earth radii, orbits far enough from its host star that it receives levels of light from its star similar to those received by Earth from the sun, said UC Berkeley graduate student Erik Petigura. He discovered the planets Jan. 6 while conducting a computer analysis of the Kepler data NASA has made available to astronomers. In order from farthest to closest to their star, the three planets receive 10.5, 3.2 and 1.4 times the light intensity of Earth, co-author Joshua Schlieder of NASA Ames Research Center calculated.

"Most planets we have found to date are scorched. This system is the closest star with lukewarm transiting planets," Petigura said. "There is a very real possibility that the outermost planet is rocky like Earth, which means this planet could have the right temperature to support liquid water oceans."

University of Hawaii astronomer Andrew Howard noted that extrasolar planets are discovered by the hundreds these days, though many astronomers are left wondering if any of the newfound worlds are really like Earth. The newly discovered planetary system will help resolve this question, he said.

"We've learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy," Howard said. "We also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron."

Kepler's K2 mission

After Petigura found the planets in the Kepler light curves, the team quickly employed telescopes in Chile, Hawaii and California to characterize the star's mass, radius, temperature and age. Two of the telescopes involved, the Automated Planet Finder on Mount Hamilton near San Jose, California, and the Keck Telescope on Mauna Kea, Hawaii, are University of California facilities.

The next step will be observations with other telescopes, including the Hubble Space Telescope, to take the spectroscopic fingerprint of the molecules in the planetary atmospheres. If these warm, nearly Earth-size planets have puffy, hydrogen-rich atmospheres, Hubble will see the telltale signal, Petigura said.

The discovery is all the more remarkable, he said, because the Kepler telescope lost two reaction wheels that kept it pointing at a fixed spot in space.

Kepler was reborn in 2014 as 'K2' with a clever strategy of pointing the telescope in the plane of Earth's orbit, the ecliptic, to stabilize the spacecraft. Kepler is now back to mining the cosmos for planets by searching for eclipses or "transits," as planets pass in front of their host stars and periodically block some of the starlight.

"This discovery proves that K2, despite being somewhat compromised, can still find exciting and scientifically compelling planets," Petigura said. "This ingenious new use of Kepler is a testament to the ingenuity of the scientists and engineers at NASA. This discovery shows that Kepler can still do great science."

Kepler sees only a small fraction of the planetary systems in its gaze: only those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are missed by Kepler. A census of Kepler planets the team conducted in 2013 corrected statistically for these random orbital orientations and concluded that one in five sun-like stars in the Milky Way Galaxy have Earth-size planets in the habitable zone. Accounting for other types of stars as well, there may be 40 billion such planets galaxy wide.

The original Kepler mission found thousands of small planets, but most of them were too faint and far away to assess their density and composition and thus determine whether they were high-density, rocky planets like Earth or puffy, low-density planets like Uranus and Neptune. Because the star EPIC-201 is nearby, these mass measurements are possible. The host star, an M-dwarf, is less intrinsically bright than the sun, which means that its planets can reside close to the host-star and still enjoy lukewarm temperatures.

According to Howard, the system most like that of EPIC-201 is Kepler-138, an M-dwarf star with three planets of similar size, though none are in the habitable zone.


Astronomers Discover Three Earth-Like Planets

Extrasolar planets are being discovered by the hundreds, but are any of these newfound worlds really like Earth? A planetary system recently discovered by the Kepler spacecraft will help resolve this question.

The system of three planets, each just larger than Earth, orbits a nearby star called EPIC 201367065. The three planets are 1.5-2 times the size of Earth, and the outermost planet orbits on the edge of the so-called “habitable zone,” where the temperature may be just right for liquid water, believed necessary to support life, on the planet’s surface.

“We’ve learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy,” explains University of Hawaii astronomer Andrew Howard. “We also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron.”

The compositions of these newfound planets are unknown. “There is a very real possibility that the outer planet is rocky like Earth,” noted Erik Petigura, a University of California, Berkeley graduate student who spent a year visiting the UH Institute for Astronomy. “If so, this planet could have the right temperature to support liquid water oceans.”

In addition to Howard and Petigura, UH graduate students Benjamin Fulton and Kimberly Aller, and UH astronomer Michael Liu are among the two dozen scientists who contributed to the study. The confirmed planets were by the NASA Infrared Telescope Facility (IRTF) and Keck Observatory in Hawaii as well as telescopes in California and Chile.

The new discovery paves the way for studies of the atmosphere of a warm planet nearly the size of Earth. The three new planets are particularly favorable for atmospheric studies because they orbit a nearby, bright star. Next, the team of astronomers that made the discovery hopes to observe the planets with the Hubble Space Telescope and other observatories to determine what elements are in the planets’ atmospheres. If Hubble finds that these warm, nearly Earth-size planets have thick, hydrogen-rich atmospheres, they will learn that there is not much chance for life.

“A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many extrasolar planets discovered by the Kepler Mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it,” says Ian Crossfield, the University of Arizona astronomer who led this study.

The discovery is all the more remarkable because Kepler is now hobbled by the loss of two reaction wheels that kept it pointing at a fixed spot in space. Kepler, launched in 2009, was reborn in 2014 as “K2” with a clever strategy of pointing the telescope in the plane of the Earth’s orbit to stabilize the spacecraft. Kepler is back to mining the cosmos for planets by searching for eclipses, or transits, as planets orbit in front of their host stars and periodically block some of the starlight.

“I was devastated when Kepler was crippled by a hardware failure,” Petigura added. “It’s a testament to the ingenuity of NASA engineers and scientists that Kepler can still do great science.” Kepler sees only a small fraction of the planetary systems in its gaze, those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are simply missed by Kepler.

“It’s remarkable that the Kepler telescope is now pointed in the ecliptic, the plane that Earth sweeps out as it orbits the Sun,” Fulton explains. “This means that some of the planets discovered by K2 will have orbits lined up with Earth’s, a celestial coincidence that allows Kepler to see the alien planets, and Kepler-like telescopes in those very planetary systems (if there are any) to discover Earth.”


Newly discovered three-planet system holds clues to atmospheres of earth-size worlds

This whimsical cartoon shows the three newly discovered extrasolar planets (right) casting shadows on their host star that can been seen as eclipses, or transits, at Earth (left). Earth can be detected by the same effect, but only in the plane of Earth’s orbit (the ecliptic). During the K2 mission, many of the extrasolar planets discovered by the Kepler telescope will have this lucky double cosmic alignment that would allow for mutual discovery—if there is anyone on those planets to discover Earth. The three new planets orbiting EPIC 201367065 are just out of alignment while they are visible from Earth, our solar system is tilted just out of their view (Image credit: K. Teramura, UH Institute for Astronomy)

Extrasolar planets are being discovered by the hundreds, but are any of these newfound worlds really like Earth? A planetary system recently discovered by the Kepler spacecraft will help resolve this question.

&ldquoWe’ve learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy,&rdquo explains University of Hawaiʻi at Mānoa astronomer Andrew Howard. &ldquoWe also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron.&rdquo

The compositions of these newfound planets are unknown. &ldquoThere is a very real possibility that the outer planet is rocky like Earth,&rdquo noted Erik Petigura, a University of California, Berkeley graduate student who spent a year visiting the UH Institute for Astronomy. &ldquoIf so, this planet could have the right temperature to support liquid water oceans.&rdquo

In addition to Howard and Petigura, UH Mānoa graduate students Benjamin Fulton and Kimberly Aller, and UH Mānoa astronomer Michael Liu are among the two dozen scientists who contributed to the study. The confirmed planets were by the NASA Infrared Telescope Facility and Keck Observatory in Hawaiʻi as well as telescopes in California and Chile.

The new discovery paves the way for studies of the atmosphere of a warm planet nearly the size of Earth. The three new planets are particularly favorable for atmospheric studies because they orbit a nearby, bright star. Next, the team of astronomers that made the discovery hopes to observe the planets with the Hubble Space Telescope and other observatories to determine what elements are in the planets’ atmospheres. If Hubble finds that these warm, nearly Earth-size planets have thick, hydrogen-rich atmospheres, they will learn that there is not much chance for life.

&ldquoA thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many extrasolar planets discovered by the Kepler Mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it,&rdquo says Ian Crossfield, the University of Arizona astronomer who led this study.

The paper presenting this work, &ldquoA Nearby M Star with Three Transiting Super-Earths Discovered by K2,&rdquo has been submitted to The Astrophysical Journal and is available for free here.


Abstract

In an effort to measure the masses of planets discovered by the NASA K2 mission, we have conducted precise Doppler observations of five stars with transiting planets. We present the results of a joint analysis of these new data and previously published Doppler data. The first star, an M dwarf known as K2-3 or EPIC 201367065, has three transiting planets ("b," with radius "c," and "d," ). Our analysis leads to the mass constraints: And M c < 4.2 M (95% confidence). The mass of planet d is poorly constrained because its orbital period is close to the stellar rotation period, making it difficult to disentangle the planetary signal from spurious Doppler shifts due to stellar activity. The second star, a G dwarf known as K2-19 or EPIC 201505350, has two planets ("b," 7.7 R and "c," 4.9 R ) in a 3:2 mean-motion resonance, as well as a shorter-period planet ("d," 1.1 R ). We find M b = , M c = and M d < 14.0 M (95% conf.). The third star, a G dwarf known as K2-24 or EPIC 203771098, hosts two transiting planets ("b," 5.7 R and "c," 7.8 R ) with orbital periods in a nearly 2:1 ratio. We find M b = and M c = . The fourth star, a G dwarf known as EPIC 204129699, hosts a hot Jupiter for which we measured the mass to be . The fifth star, a G dwarf known as EPIC 205071984, contains three transiting planets ("b," 5.4 R "c," 3.5 R and "d," 3.8 R ), the outer two of which have a nearly 2:1 period ratio. We find M b = , M c < (95% conf.) and M d < 35 M (95% conf.).


New Star On The Block

Despite having lost some of it's critical guidance systems, NASA's Kepler Space Telescope recently located a star with three orbiting planets, each of which is similar in size to Earth.

The star has been registered as EPIC 201367065 and is about half the size and mass of our own sun. It is 150 light years from Earth and is bright enough for astronomers to study its orbiting planets' atmospheres and compare them to that of Earth. Since these planets exist in the "Goldilocks" zone, where surface temperatures are close to "just right" and make the existence of life and liquid water possible, scientists are excited about learning more about them.

The three planets are 2.1, 1.7 and 1.5 times the size of Earth. The outermost planet, at 1.5 Earth radii, is the smallest of the group and orbits far enough from its host star that it receives levels of light from its star similar to those received by Earth from the sun. UC Berkeley graduate student Erik Petigura discovered the planets early in January while conducting a computer analysis of Kepler data made available to researchers by NASA. He calculated that the three planets receive 10.5, 3.2, and 1.4 times the light intensity of Earth.

"Most planets we have found to date are scorched. This system is the closest star with lukewarm transiting planets," Petigura said. "There is a very real possibility that the outermost planet is rocky like Earth, which means this planet could have the right temperature to support liquid water oceans."

Still more analysis and observation is necessary to know if these planets are at all like Earth. Other telescopes, including the Hubble Space Telescope, will be needed to get see the types of molecules in the planets' atmospheres. If the planets are like others discovered recently and shrouded in puffy hydrogen-rich clouds the Hubble will be able to read the spectrometry of that, said Petigura.

Petigura said that the discovery was even more significant because the Kepler telescope lost two reaction wheels that kept it focused on a specific fixed point in space. NASA corrected this by changing the aim of the telescope to Earth's elliptical plane. "This discovery proves that K2, despite being somewhat compromised, can still find exciting and scientifically compelling planets," said Petigura. "This ingenious new use of Kepler is a testament to the ingenuity of the scientists and engineers at NASA. This discovery shows that Kepler can still do great science."

Before losing the guidance system in the original mission, the Kepler Space Telescope found thousands of small planets, but most of them were too faint and far away to assess their density and composition. Without knowing the molecular make up of a planet's atmosphere, whether is high density and rocky like Earth or high-density, or puffy and low-density planets like Uranus and Neptune, scientists are unable to determine if the planet could support life, a crucial determination in astronomy. Because the star EPIC-201 is nearby, these mass measurements are possible. It is also less intrinsically bright than the sun, which means that its planets can reside close to the host-star and still enjoy lukewarm temperatures.

Co-authors of the paper "Nearby M Star With Three Transiting Super-Earths Discovered by K2" include Joshua Schlieder of NASA Ames Research Center and colleagues from Germany, the United Kingdom and the United States.


Three Nearly Earth-size Planets Found Orbiting Nearby Star

NASA's Kepler Space Telescope, despite being hobbled by the loss of critical guidance systems, has discovered a star with three planets only slightly larger than Earth.

The outermost planet orbits in the "Goldilocks" zone, a region where surface temperatures could be moderate enough for liquid water and perhaps life to exist.

The star, EPIC 201367065, is a cool red M-dwarf about half the size and mass of our own sun. At a distance of 150 light years, the star ranks among the top 10 nearest stars known to have transiting planets. The star's proximity means it's bright enough for astronomers to study the planets' atmospheres to determine whether they are like Earth's atmosphere and possibly conducive to life.

"A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many exoplanets discovered by the Kepler mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it," said Ian Crossfield, the University of Arizona astronomer who led the study.

A paper describing the find by astronomers at the University of Arizona, University of California, Berkeley, University of Hawaii, Manoa, and other institutions has been submitted to Astrophysical Journal and is freely available on the arXiv website.

The three planets are 2.1, 1.7 and 1.5 times the size of Earth. The outermost planet, at 1.5 Earth radii, is the smallest of the bunch and orbits far enough from its host star that it receives levels of light from its star similar to those received by Earth from the sun, said UC Berkeley graduate student Erik Petigura, who discovered the planets Jan. 6 while conducting a computer analysis of the Kepler data NASA has made available to astronomers. He calculated that the three planets receive 10.5, 3.2, and 1.4 times the light intensity of Earth.

"Most planets we have found to date are scorched. This system is the closest star with lukewarm transiting planets," Petigura said. "There is a very real possibility that the outermost planet is rocky like Earth, which means this planet could have the right temperature to support liquid water oceans."

University of Hawaii astronomer Andrew Howard noted that extrasolar planets are discovered by the hundreds these days, though many astronomers are left wondering if any of the newfound worlds are really like Earth. The newly discovered planetary system will help resolve this question, he said.

"We've learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy," Howard said. "We also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron."

After Petigura found the planets in the Kepler light curves, the team quickly employed telescopes in Chile, Hawaii and California to characterize the star's mass, radius, temperature, and age. Two of the telescopes involved, the Automated Planet Finder on Mount Hamilton near San Jose, Calif., and the Keck Telescope on Mauna Kea, Hawaii, are University of California facilities.

The next step will be observations with other telescopes, including the Hubble Space Telescope, to take the spectroscopic fingerprint of the molecules in the planetary atmospheres. If these warm, nearly Earth-size planets have puffy, hydrogen-rich atmospheres, Hubble will see the telltale signal, Petigura said.

The discovery is all the more remarkable, he said, because the Kepler telescope lost two reaction wheels that kept it pointing at a fixed spot in space. Kepler was reborn in 2014 as 'K2' with a clever strategy of pointing the telescope in the plane of Earth's orbit, the ecliptic, to stabilize the spacecraft. Kepler is now back to mining the cosmos for planets by searching for eclipses or "transits," as planets pass in front of their host stars and periodically block some of the starlight.

"This discovery proves that K2, despite being somewhat compromised, can still find exciting and scientifically compelling planets," said Petigura. "This ingenious new use of Kepler is a testament to the ingenuity of the scientists and engineers at NASA. This discovery shows that Kepler can still do great science."

Kepler sees only a small fraction of the planetary systems in its gaze: those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are missed by Kepler. A census of Kepler planets that the team conducted in 2013 corrected statistically for these random orbital orientations, and concluded that one in five sun-like stars in the Milky Way Galaxy have Earth-size planets in the habitable zone. Accounting for other types of stars as well, there may be 40 billion such planets galaxywide.

The original Kepler mission found thousands of small planets, but most of them were too faint and far away to assess their density and composition and thus determine whether they were high-density, rocky planets like Earth or puffy, low-density planets like Uranus and Neptune. Because the star EPIC-201 is nearby, these mass measurements are possible. The host star, an M-dwarf, is less intrinsically bright than the sun, which means that its planets can reside close to the host-star and still enjoy lukewarm temperatures.

According to Howard, the system most like that of EPIC-201 is Kepler-138, an M-dwarf star with three planets of similar size, though none are in the habitable zone.

Co-authors of the paper "Nearby M Star With Three Transiting Super-Earths Discovered by K2" include Joshua Schlieder of NASA Ames Research Center and colleagues from Germany, the United Kingdom and the United States.


Watch the video: Space Engine Planet Epic 201367065 d. k2-3 d (July 2022).


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