We are searching data for your request:
Upon completion, a link will appear to access the found materials.
I see that there are a number of stars that have a number at the end of them. Ross 128 is an example. What does this number mean?
The number refers to the number in the catalog compiled by Frank Elmore Ross. From the Wikipedia article on Ross
At Yerkes Observatory he was the successor to the late E. E. Barnard, inheriting Barnard's collection of photographic plates. Ross decided to repeat the same series of images and compare the results with a blink comparator. In doing so, he discovered 379 new variable stars and over 1000 stars of high proper motion. Some of the high-proper motion stars turned out to be quite nearby, and many of these stars (such as Ross 154) are still widely known by the catalog number he gave them.
Adding to answer by John Holtz. Ross compiled a catalog of high proper motion stars (stars that move relatively rapidly against background stars). The numbers are in order of increasing Right Ascension (sky coordinate like longitude). The list doesn't start at zero RA. Number 5 is just above zero. See the first list of the catalog: Ross, Frank, E., 1925, Astronomical Journal v36, p96
A nearby Earth-sized planet has been found… and it *may* be a nice place to live
Oh, this is very interesting exoplanet news indeed: Astronomers have found a planet that is likely around the same size as Earth, and it's orbiting a star that's only 11 light years away! Better yet, depending on the planet's characteristics, it could have temperate conditions on the surface. In other words, it may be — may be — Earth-like.
The planet orbits Ross 128, a cool red dwarf star. The star is something of a dim bulb it has a sixth the mass of the Sun, and shines only about 0.004 times as brightly. Even though it's close (it's the 14th closest known stellar system to ours, including brown dwarfs) it's so faint you need a telescope to see it. At a magnitude of 11.5, the dimmest star you can see with your naked eye is still 100 times brighter than Ross 128!
More Bad Astronomy
This makes it a tough star to study. Looking for planets around it takes a big telescope and sensitive equipment. The planet, called Ross 128 b, was found using what's called reflexive motion. As it orbits the star, the gravity of the planet pulls back on the star. While the planet makes a big circle, the star makes a smaller one. As that happens, sometimes the star is approaching Earth, and sometimes moving away. That causes the starlight from it to shift in color very slightly (via the Doppler shift).
Two objects of different masses orbit each other the more massive one makes a little circle and the lower mass one a bigger circle. Credit: NASA/Spaceplace
This is a very small effect, but it's measurable. Astronomers used the High Accuracy Radial velocity Planet Searcher to observe the star 157 times over nearly 12 years. They then checked the signal to see if there was a periodic shift in the star's light… and there was!
The period of the shift was about 9.9 days, which is therefore the orbital period of the planet: Its year. That means it huddles close to the star, about 7.4 million kilometers out. The Earth's orbit is 150 million km from the Sun, but again remember Ross 128 is a pretty feeble thing! When you account for the orbital size and stellar output, the planet gets about 1.4 times as much sunlight as Earth does.
The temperature of the planet, though, isn't possible to know accurately. If it's dark, it absorbs more light from the star and is warmer. If it's shinier it reflects more light, and will be colder. If it has an Earth-like reflection (absorbing about 60% of the Sun's light and reflecting 40%) then it will have a temperature of roughly 0° Celsius. That's cold, but remember, that's average. The Earth's average temperature is only 16°C, but the variations are pretty big.
And the planet could be darker than Earth, making it warmer. Of course, it could be more reflective, in which case it's an iceball. We just don't know.
Artwork depicting Ross 128 and its planet. Credit: ESO/ M. Kornmesser
We have a better understanding of its mass. That comes from how hard it pulls on its parent star, and that comes out to be about 1.4 times Earth's mass. Unfortunately, that's a lower limit. It could be higher, though how much isn't known.
Still, that's not a deal breaker for a planet. Earth is pretty dense. A planet less dense but bigger than Earth would have more mass, yet conditions on the surface (meaning gravity) would be roughly Earth-like.
Again, we don't know. But this is fairly promising!
Even better news is that the star looks to be stable. Some red dwarfs have very strong magnetic fields, and can have pretty intense stellar activity like flares. The nearest star to ours, Proxima Centauri, has an Earth-sized planet as well, but Proxima is an active star. It has flares so intense they could damage the potential ecosystem of the planet.
That won't be the case with Ross 128. It's a slow rotator (it spins once every 121 days), and magnetic field strength is generally tied to rapid spinning (the magnetic field is generated deep inside the star by its spin). The observations showed only weak activity from the star, so that's nice.
Slow rotation is also usually an indicator of age, and a different study (in that link it's listed in Table 7 under Gl 447, another name for the star) shows Ross 128 to be about two billion years old. That's half the age of our solar system, but long enough for a planet to develop life (by that age, Earth was covered in goo).
All in all, this is a very interesting planet. We don't know if it's Earth-like, but given what we do know I don't see any show stoppers to preclude it. And it's close by! One of the reasons these observations were done was to look for Earth-sized planets around nearby red dwarfs, so that future large telescopes can look for signs of atmospheres around them. Ross 128 b is a solid candidate for that.
… and if you're patient, it gets easier. Ross 128 is what's called a high proper motion star it's apparently moving across the sky relatively rapidly due to it being close to us. When you project its motion into the future it turns out that in about 70,000 years it'll be the closest star to Earth! That means Ross 128 b will be the closest exoplanet to us as well.
That'll make telescopic observations of it easier, and cut down any travel time to it by a factor of two or so. I don't think that last bit will help much though.
But that underscores an important aspect of this: Red dwarf stars are by far the most common kind of star in the galaxy. And two of the nearest have Earth-sized planets! Extrapolating from a small sample size is tricky, but that seems to me a strong indicator that there are a lot of planets like this in the Milky Way. Billions. Maybe tens of billions. More.
If Earth is rare, say one in a million, then this alone implies there are thousands of Earth-like planets in the galaxy. We don't know for sure yet, but we're getting close to having a handle on this number.
Ross 128 Mystery Signals Aren't From Aliens. But What Would Happen If They Were?
Astronomers working at the Arecibo radio telescope in Puerto Rico have detected a weird radio signal, spotted when pointing their telescope at the nearby star Ross 128. They're not getting too excited about the prospect of an alien civilization contacting us just yet though. "In case you are wondering, the recurrent aliens hypothesis is at the bottom of many other better explanations," said Abel Mendez, the scientist leading the campaign.
Of course, this doesn't stop others speculating that the signal may be just that. And it begs the question, how do you work out if a strange signal from space really is a message from aliens? The simple answer is that you have to rule out everything else first and only then can you think it may be aliens. As Sherlock Holmes said: "When you have eliminated the impossible, whatever remains, however improbable, must be the truth." But eliminating all the other possibilities isn't exactly easy.
When radio pulsars were first detected in 1967, "little green men" were at least considered a possibility&mdashbefore it was that they are rapidly rotating neutron stars. The discovery opened up a whole new area of astrophysics, so could hardly be considered a disappointment.
There have been other cases. In 1977, astronomers detected a radio burst dubbed the "WOW signal"&mdashand they have been debating its origin for decades. Only recently was it suggested that there could be a natural explanation: emission from a passing comet that happened to lie in the right part of the sky. However, other astronomers have cast doubt on the comet idea, so it can't be considered to be settled just yet.
Another mysterious signal is that from Tabby's star, which displays strange quasi-periodic dips in its brightness. Could this be evidence of orbiting alien megastructures, or is it merely a cloud of natural debris surrounding the star? Once again, the jury is still out on that one, but we have certainly not ruled out all natural possibilities yet.
The signal seen from Ross 128, which is 11 light years from Earth, consisted of quasi-periodic radio pulses across a wide range of frequencies. The observations were made on 12 May in the range 4-5 GHz and lasted about 10 minutes. A periodic signal naturally draws attention to itself and could indicate an artificial origin. However, some natural processes can give rise to periodic signals too. The pulses could be due to something like solar flares coming from the red dwarf star (a small and relatively cool star). Such stars are indeed prone to this type of activity, but the researchers say the radio pulses are unlike anything ever seen from other similar stars.
Perhaps more likely is that the signals originate closer to home&mdasharising as interference from a high altitude, Earth-orbiting artificial satellite which happened to pass through the field of view of the telescope during the observations. However, such a signal from a satellite has not been seen before either. The Arecibo team are planning further observations to try and check these possibilities.
Exoplanets and Life
So, what are the chances the signal is evidence of aliens? The last 20 years have seen an explosion in the number of planets found orbiting other stars. It is likely that a large proportion of the stars in the Milky Way harbor habitable exoplanets, yet we still have no evidence of life elsewhere.
The lack of evidence for extraterrestrial life lies at the heart of the Fermi paradox. Simply put, if planets and life are common in the galaxy, why have we not found aliens yet?
My best guess, based on what we now know, is that simple life may well be common&mdashthere are probably billions of Earth-like planets out there, so it is almost inconceivable that life has only evolved on one of them. However, intelligent, communicating life may well be extremely rare&mdasheither because it doesn't arise or because when it does, it gets wiped out fairly quickly. This idea is known as the great filter.
The best chance of spotting life in the galaxy may therefore not come from looking for radio signals, but from looking for the signature of a biosphere as an exoplanet transits across the face of its star.
By measuring the spectrum (breakdown of light according to wavelength) of a star while its planet passes in front, then subtracting the spectrum of the star seen alone, any tiny difference must be due to the signature of the planet's atmosphere. This signature could reveal the presence of gases like oxygen and methane, which may mean the planet hosts life&mdashalthough this may just be microbes. But it may indeed be our best bet to find life in the galaxy.
What If You Do Spot an Alien Signal?
Let's return to the signal from Ross 128. What if the astronomers at Arecibo rule out solar flares and artificial satellites as the origin of the signal? The problem is, we can only rule out the things we know about. So even if these possibilities are discounted, there may still be other causes that have not been thought of yet. In fact, this is how all science works. We can't ever claim anything is definitely true, we can only rule out the things that are false and make a hypothesis that something else is true until proved otherwise.
But that doesn't mean that we can't one day receive a signal that is unambiguously of alien origin. If a signal is received with such a high level of structured information that it can't be a natural signal, then there may be no other explanation.
In this case, the Search for Extra Terrestrial Intelligence (SETI), have clear protocols for what happens next. These specify that the discoverer must notify other signatories to the protocols, other astronomers around the world, and also the United Nations. All data surrounding the discovery must also be made public. Importantly, no response to the signal should be sent until international consultations have taken place. Whatever (if anything) is transmitted back in the direction the signal came from would indicate our presence, so we'd better be sure we want to announce our existence before doing so.
Maybe one day these protocols will be invoked, but until then, astronomers will keep looking for more prosaic explanations for all the weird signals they detect.
Andrew Norton is Professor of Astrophysics Education at The Open University
Habitable Planet Reality Check: The Nearby Ross 128
The year 2017 is certainly proving to be a fertile one for the discovery of potentially habitable exoplanets. Just a year ago there were maybe five exoplanets identified as having genuinely good prospects of being potentially habitable (see “Top Five Known Potentially Habitable Planets”) and only one of them, Proxima Centauri b discovered in 2016, was relatively nearby (see “Proxima Centauri b: The Search for More Exoplanets Continue”). Over the last several months, that list has expanded significantly as a result of a number of ongoing surveys taking place around the globe and in space. New additions to the list of nearby potentially exoplanets from 2017 include possibly three out of the seven exoplanets found orbiting TRAPPIST-1 along with individual exoplanets found orbiting GJ 273 and LHS-1140 (see “Habitable Planet Reality Check: The Seven Planets of TRAPPIST-1”, “Habitable Planet Reality Check: The Nearby GJ 273 or Luyten’s Star” and “Habitable Planet Reality Check: A Super-Earth Orbiting the Nearby LHS 1140”). While still far too distant to reach with today’s technology, these nearby exoplanets would be potential targets of exploration if interstellar travel proves to be practical in the future.
Now the European team of astronomers operating the HARPS (High Accuracy Radial velocity Planet Search) spectrograph attached to the European Southern Observatory’s (ESO’s) 3.6-meter telescope in La Silla, Chile have announced the discovery of yet another potentially habitable exoplanet as a result of their long-term survey of nearby stars. In a paper to be published in the peer-reviewed European astronomical journal, Astronomy & Astrophysics, with Xavier Bonfils (currently at Université Grenoble Alpes) as the lead author, the HARPS team describes their latest find – a temperate, roughly Earth-mass object found orbiting the nearby star commonly known as Ross 128. So what are the prospects for the potential habitability of this new exoplanet given what we now know about it?
The star Ross 128 is an V magnitude 11.1 star located in the constellation of Virgo – The Virgin. Its common name is derived from being the 128 th star cataloged by American astronomer Frank E. Ross (1874-1960) during his early work at the Yerkes Observatory while searching for and characterizing dim variable stars. First appearing as part of the fourth installment of Ross’ catalog published in 1926, subsequent work showed it to be an intrinsically dim, nearby red dwarf star with a distance currently pegged at 11.02±0.02 light years based on the initial astrometric measurements from the ESA Gaia mission. This makes Ross 128 the 12 th closest known star system to the Sun. Because of its closeness, Ross 128 was included in the first edition of the Gliese Catalogue of Nearby Stars in 1957 earning it the designation of GJ 477 after the creator of the catalog, German astronomer Wilhelm Gliese (1915-1993), and his long time collaborator on later editions, Hartmut Jahreiß.
American astronomer Frank E. Ross (shown here with the famous 40-inch Yerkes refractor in 1925) first cataloged Ross 128 in 1926. (Lick Observatory)
According to the best data available on Ross 128 compiled by Bonfils et al., this spectral type M4V red dwarf has a radius of 0.197±0.008 times that of the Sun and a surface temperature 3192±60 K. The luminosity is calculated to be 0.0036±0004 times that of the Sun and the mass is estimated to be 0.17±0.02 times. Occasional flares have been noted for this star over the decades which can dramatically increase its brightness for periods of several minutes earning it the variable star designation of FI Virginis. But based on a detailed analysis of its activity compared to other red dwarf stars, Ross 128 seems to be among the least magnetically active red dwarfs currently known suggesting that it is a fairly evolved object. This low level of activity combined with its Sun-like metallicity, its orbit around the galaxy and its long rotation period estimated to be about 121 days all suggest an age well in excess of five billion years.
This chart shows the location of Ross 128 in the constellation of Virgo. Click on image to enlarge. (ESO, IAU and Sky & Telescope)
Like many nearby stars, Ross 128 has been the target of exoplanet searches for decades. The most sensitive search results previously published were from an analysis of HARPS radial velocity (RV) measurements published in 2013 again with Xavier Bonfils (then with Observatoire de Genève) as the lead author. With only a half dozen measurements available at the time, the star’s RV seemed to vary on the order of a meter per second suggesting that the reflex motion of an exoplanet orbiting Ross 128 was being observed although it was impossible to claim a definitive exoplanet detection or characterize its properties with so little data. With this promising start, additional precision RV measurements were made by the HARPS team over the following years.
The ESO 3.6m Telescope equipped with HARPS was used to acquire the data used to find the new planets orbiting Ross 128. (ESO/H.H.Heyer)
For their most recent work, Bonfils et al. started with a total of 157 precision RV measurements made of Ross 128 using HARPS between July 2, 2005 and April 26, 2016. Because of an upgrade to the HARPS spectrograph’s fiber optic feed introduced in May 2015 which significantly altered the line spread function (as well as improve the instrument measurement stability), the two parts of the RV data were processed separately using the team’s proven set of data reduction tools to find a clear signal with a period of about 9.9 days. Detailed modelling of the data assuming various sources of natural and instrument noise found a well-sampled periodic signal in the RV measurements with a semiamplitude of 1.7 meters per second consistent with the presence of an exoplanet in a circular orbit with a period of 9.86 days. Plugging in the properties of the star itself yields a mean orbital radius of 0.049 AU (just 7.3 million kilometers) and a MPsini of 1.35 times that of the Earth (or ME) for the exoplanet. Since the inclination of its orbit to the plane of the sky, i, is not currently known, the actual mass, MP, of what is now designated Ross 128b will almost surely be larger. The amount of energy Ross 128b receives from its host star, the effective stellar flux of Seff, is about 1.38 times that of the Earth based on these derived properties.
The top panel shows the HARPS radial velocity (RV) data folded in phase space for the orbit of Ross 128b while the lower panel shows the residuals after the orbit fit. The orange and blue data points show the RV measurement before and after the HARPS upgrade, respectively, while the gray band indicates the best fit for the data. Click on image to enlarge. (Bonfils et al.)
In order to help eliminate the possibility that the observed variations in RV were not some form of stellar activity mimicking a planetary signature, Bonfils et al. also analyzed two sets of photometric data for Ross 128. They secured over nine years of ground-based V-band brightness measurements made by the All Sky Automated Survey (ASAS) and 82 days of almost continuous precision photometry obtained by NASA’s Kepler spacecraft as part of Campaign 1 of its extended K2 mission running from June to August 2014 (see “The First Year of Kepler’s K2 Mission”). There was no hint of any photometric variability corresponding to the ten-day period of Ross 128b strengthening the case that this is a planet.
After taking into account the effects of Ross 128b on the precision RV measurements, the only other significant signals were found to have periods of about 123 and 52 days. The ASAS photometry of Ross 128 clearly displays regular variations with a period of 121 days corresponding to the rotation of the star (the K2 photometry could not used in this assessment since it did not cover a complete rotation). The 123-day periodicity in the RV data is clearly associated with stellar activity modulated by the rotation of the star with the slight variance with 121-day period found in the photometry probably being due to differential rotation. The 52-day periodicity is explained as aliasing of half the 123-day signal caused by the annual gaps in the HARPS data set. While no other convincing exoplanet candidates can be identified in the current set of RV measurements, there could easily be additional members of this system awaiting discovery.
A thorough assessment of the habitability of any extrasolar planet would require a lot of detailed data on the properties of that planet, its atmosphere, its spin state, the evolution of its volatile content and so on. Unfortunately, at this very early stage, the only information typically available to scientists about extrasolar planets are basic orbit parameters, a rough measure of its size and/or mass and some important properties of its sun. Combined with theoretical extrapolations of the factors that have kept the Earth habitable over billions of years (not to mention why our neighbors are not habitable today), the best we can hope to do at this time is to compare the known properties of extrasolar planets to our current understanding of planetary habitability to determine if an extrasolar planet is “potentially habitable”. And by “habitable”, I mean in an Earth-like sense where the surface conditions allow for the existence of liquid water – one of the presumed prerequisites for the development of life as we know it. While there may be other worlds that might possess environments that could support life, these would not be Earth-like habitable worlds of the sort being considered here.
The first step in assessing the potential habitability of Ross 128b is to determine what sort of world it is: is it a rocky planet like the Earth or is it a volatile-rich mini-Neptune possessing a deep hot atmosphere dominated by hydrogen overlaying layers of exotic high temperature ices with little prospect of being habitable in an Earth-like sense? Unfortunately, the only information currently available about this new exoplanet that could help make such an assessment is its Mpsini or minimum mass value. The actual mass and the radius of Ross 128b are needed to calculate this exoplanet’s density and help constrain its bulk composition.
With such a tight orbit around its sun, Ross 128b has about a 2% probability that the plane of its orbit is oriented by random chance to produce transits observable from Earth. Such transits could be used to pin down the orbit inclination, i, allowing the actual planet mass to be determined as well as measure the exoplanet’s radius. Unfortunately, there were no hints of such transits found in Kepler’s K2 photometry from 2014. Any transiting exoplanet passing directly in front of Ross 128 as viewed from our solar system with a radius larger than 0.19 times that of the Earth would have been detected to a 99% confidence level. Grazing transits of exoplanets closer to Earth in size have also been excluded to high confidence.
This plot shows Kepler’s photometric data phase folded for the orbit of Ross 128b with the expected signature of an exoplanet with the Earth’s radius and half that value. Click on image to enlarge. (Bonfils et al.)
Bonfils et al. openly discuss the possibility of using the 39-meter European Extremely Large Telescope (E-ELT) currently under construction for ESO on top of Cerro Armazones in northern Chile to observe Ross 128b after it is commissioned in 2024. The large size of this telescope combined with the latest adaptive optics technology (no to mention the superb seeing in Chile’s Atacama Desert) should allow Ross 128b to be resolved at its maximum elongation distance of just 15 milliarc seconds from its host star. Combined with an appropriately designed high spectral dispersion instrument which allows selection of bands to improve the contrast ratio (i.e. the ratio of the apparent brightness of the host star and its orbiting planet) and ease detection through the glare of the host star, Bonfils et al. believe that Ross 128b could be directly detected almost as easily as Proxima Centauri b (an exoplanet that has already been studied in detail as a prospective future E-ELT target).
This artist’s impression shows the European Extremely Large Telescope (E-ELT) in its enclosure. The E-ELT could provide spectral images of nearby exoplanets like Ross 128b after it is commissioned in 2024. (ESO/L. Calçada)
In addition to providing vital spectral information about the world, the orbit inclination could be determined using E-ELT observations. If E-ELT proves incapable of making the required observations, 10+ meter-class space-based telescope built with features specifically to support exoplanet detection should be able to make the required observations in the next decade. While these sort of observations can be used to help constrain the radius of Ross 128b, direct measurements of its size will likely require a space-based interferometer of the sort that will probably not be available until mid-century.
While we wait until measurements such as these come from E-ELT or other proposed instruments in the next decade, statistical arguments can be made about the probability this new exoplanet has a rocky composition. An analysis of the mass-radius relationship for extrasolar planets smaller than Neptune performed by Rogers strongly suggests that the population of known exoplanets transitions from being predominantly rocky planets like the Earth to predominantly volatile-rich worlds like Neptune at radii no greater than 1.6 times that of the Earth or RE but more likely at 1.5 RE (see “Habitable Planet Reality Check: Terrestrial Planet Size Limit”). While rocky planets larger than this are possible, they become more uncommon with increasing radius. A planet with a radius of 1.6 RE and an Earth-like composition would have a mass of about 6 ME. With its currently unconstrained orbit inclination, there is about a 3% chance that Ross 128b, with a MPsini of 1.35 ME, exceeds this 6 ME threshold.
More recent work by Chen and Kipping with a larger sample of exoplanets suggests that the gradual transition of the exoplanetary population from predominantly rocky planets to volatile-rich worlds starts at about 2 ME. There is about a 26% chance that Ross 128b exceeds this threshold suggesting that it has a small but non-zero chance of being a mini-Neptune. Until a more quantitative estimate can be made based on an analysis of the available data, it seems likely (but not certain) that Ross 128b is a rocky planet with a bulk composition probably not too dissimilar from Earth’s.
Another important criterion which can be used to determine if a planet is potentially habitable is the amount of energy it receives from its parent star known as the effective stellar flux or Seff. According to the work by Kopparapu et al. (2013, 2014) on the limits of the habitable zone (HZ) based on detailed climate and geophysical modeling, the inner limit of the HZ is conservatively defined by the runaway greenhouse limit where a planet’s temperature would soar even with no CO2 present in its atmosphere resulting in the loss of all of its water in a geologically brief time in the process. For an Earth-size planet orbiting Ross 128, this happens at an Seff value of 0.93 which corresponds to a mean orbital distance of 0.063 AU. With a Seff calculated to be 1.38, Ross 128b orbits too close to its sun to be considered habitable by this definition. However, there are other definitions for the HZ worth considering for this case.
Because of the tight orbit of Ross 128b and its age, it would be expected to be a synchronous rotator which keeps the same side pointing towards its sun. Detailed climate modeling over the last two decades shows that synchronous rotation is not the impediment to global habitability as it was once thought. In fact, it has been shown that slow or synchronous rotation can actually result in an increase of the Seff for the inner edge of the HZ owing to feedback mechanisms which result in the formation of a reflective cloud layer on the daylight side. According to the recent work by Yang et al., the inner edge of the HZ for a slow rotator orbiting a star like Ross 128 would have an Seff of 1.58 corresponding to an orbital distance of just 0.048 AU. This places Ross 128b comfortably inside the HZ for synchronous rotators.
But before we invest too much into this result, a more recent paper by Kopparapu et al. (2016) which takes into account the effects of short orbital periods on atmospheric circulation also suggests that the feedback mechanism that maintains the reflective cloud layer on the daylight side starts to breakdown for synchronously rotating exoplanets in tight orbits. This is due to the Coriolis effect which breaks up this dayside cloud layer resulting in a moist runaway greenhouse effect at lower Seff values than found by Yang et al.. For a cool star like Ross 128, the Seff for the inner edge of the HZ would be about 1.23. An even more recent paper by Kopparapu et al. (2017) which incorporate the latest data of how key greenhouse gases transmit and absorb infrared radiation suggests that changes in the atmospheric structure can lead to rapid and permanent water loss for an Earth-size exoplanet at an Seff of around 1.20 even before a runaway greenhouse effect sets in. Although Ross 128 is a relatively quiescent red dwarf today, various forms of elevated activity it would have surely experienced earlier in its life would be yet another loss mechanism that would exacerbate the situation. With the permanent loss of water, the carbonate-silicate cycle which helps act as a global thermostat breaks down allowing CO2 to build up in the atmosphere resulting in a dry runaway greenhouse much as Venus experiences today in our own solar system.
This artist’s impression shows a temperate version of Ross 128 b, with its red dwarf parent star in the background. (ESO/M. Kornmesser)
Given the uncertainties in the various red dwarf HZ models currently available, it seems that it is a toss up as to whether or not Ross 128b orbits inside the HZ although the situation does not appear especially promising at the moment. For this reason, Bonfils et al. characterize Ross 128b as a “temperate planet” instead of a “habitable planet”. There are possible “temperate” scenarios where an exoplanet could be stripped of most of its volatiles (including excess amounts of greenhouse gases like water and CO2) early in its evolution leaving an arid desert world which might have some environments which could support life – essentially hot versions of Mars sharing its thin atmosphere and hyperarid surface conditions. But such scenarios, if they prove to be physically plausible, would probably start deviating too much from Earth-like habitability being considered in this assessment. More detailed models specifically for Ross 128b will surely become available in the near future to address this exoplanet’s possible evolutionary paths and shed more light on its potential habitability.
The discovery of Ross 128b is especially exciting since it provides astronomers with yet another opportunity to study a nearby exoplanet in detail with the next generation of astronomical instruments. Based on what little we know at this time about this newly discovered exoplanet, the odds seem to favor it being a rocky world like the inner planets of our own solar system. But given the high effective stellar flux and the current uncertainties in the various HZ models for red dwarfs, the best we can hope to claim at this stage is that this newly discovered exoplanet orbits somewhere near the inner edge of the HZ – maybe just inside the HZ as a warm yet habitable exoplanet but maybe more likely just outside the HZ to become a non-habitable Venus-like world.
Based on this assessment, it seems that Ross 128b has only moderate chances of being potentially habitable in an Earth-like sense – certainly not as good as the prospects for red dwarf exoplanets like Proxima Centauri b, GJ 273b or LHS-1140b but definitely better than those for the recently discovered GJ 625 (see “Habitable Planet Reality Check: Is GJ 625b a Super-Earth or a Super-Venus”). Fortunately, future observations of Ross 128b will help provide vital data for its current state allowing HZ models to be validated. And there still remains the possibility of additional exoplanets in this system including in more distant orbits comfortably inside of the habitable zone. Regardless of whether or not Ross 128b is potentially habitable, it is most definitely an exoplanet worthy of further detailed study.
This brief ESO video provides an artist’s impression of what Ross 128b might look like.
For a complete collection of articles about our other neighboring star systems and the searches for exoplanets orbiting them, see Drew Ex Machina’s page on Nearby Stars.
X. Bonfils et al., “The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample”, Astronomy & Astrophysics, Vol. 549, ID A8, January 2013
Xavier Bonfils et al., “A Temperate exo-Earth around a quiet M dwarf at 3.4 parsecs”, arXiv 1711.06177 (accepted by Astronomy & Astrophysics), November 16, 2017 [Preprint]
Jingjing Chen and David Kipping, “Probabilistic Forecasting of the Masses and Radii of Other Worlds”, The Astrophysical Journal, Vol. 834, No. 1, Article id. 17, January 2017
R. K. Kopparapu et al., “Habitable zones around main-sequence stars: new estimates”, The Astrophysical Journal, Vol. 765, No. 2, Article ID. 131, March 10, 2013
Ravi Kumar Kopparapu et al., “Habitable zones around main-sequence stars: dependence on planetary mass”, The Astrophysical Journal Letters, Vol. 787, No. 2, Article ID. L29, June 1, 2014
Ravi Kumar Kopparapu et al., “The Inner Edge of the Habitable Zone for Synchronously Rotating Planets around Low-mass Stars Using General Circulation Models”, The Astrophysical Journal, Vol. 819, No. 1, Article ID. 84, March 2016
Ravi Kumar Kopparapu et al., ” Habitable Moist Atmospheres on Terrestrial Planets near the Inner Edge of the Habitable Zone around M Dwarfs”, The Astrophysical Journal, Vol. 845, No. 1, Article ID. 5, August 2017
Leslie A. Rogers, “Most 1.6 Earth-Radius Planets are not Rocky”, The Astrophysical Journal, Vol. 801, No. 1, Article id. 41, March 2015
Jun Yang et al., “Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate”, The Astrophysical Journal Letters, Vol. 787, No. 1, Article id. L2, May 2014
“Closest Temperate World Orbiting Quiet Star Found”, ESO Press Release 1736, November 15, 2017 [Press Release]
When do we leave?
Well, we don’t have to, really. Ross 128 is so excited to meet us that it’s coming our way. The orbit has the exoplanet and its parent star moving closer to us and in the blink of a cosmic eye (that’s 79,000 Earth years, technically), it will be our nearest stellar neighbor. That gives us time to speed up our rockets (and maybe invent Star Trek’s warp drive). Ross 128, again, is 11 light years away. For the sake of context, the moon — currently reachable by way of a three-day trip — is just 1.3 light seconds away.
November 17, 2017 at 6:43 pm
Mr. Bochanski would profit from a proofreader.
In his interesting November 15, 2017 article in Sky & Telescope, he’s offered what is basically a first draft. The article is entitled: “Planet Orbits Quiet Star 11 Light-years Away.”
The first passage worth noting is:
“At a distance of 11 light-years, Ross 128 is the 12th closest star to the Sun. Like Proxima Centauri, it’s an M-class star with about 16% the Sun’s mass.
As a matter of rhetoric (not grammar), it would have been smoother if he had named the subject of his article, Ross 128, before going into detail about the class and size.
“Like Proxima Centauri, it’s an M-class star with about 16% the Sun’s mass.”
Since Mr. Bochanski refers to the Sun for comparison, it seems an omission to NOT mention that the Sun is a G Class star.
“We now know that small rocky planets like our Earth are common and that the most common type of star (M dwarfs) is the most likely hosts for planets.”
It would have improved clarity to state the average mass of M Class stars (0.3 of our Sun) for completeness, again, since he was comparing 128 Ross to the Sun.
A more serious problem related to accuracy, and it occurred with the following statement:
“(128 Ross) hugs its star more tightly than in the solar system because of the star’s low luminosity. "
1. It is not IN our Solar System. That should have been re-written.
2. The use of the word “because” is flat out wrong. This creates a false cause-and-effect relationship. The close orbit is not BECAUSE OF the low luminosity. Nor is the low luminosity related to the close orbit.
Then he writes: “…Because Ross 128 is small and cool compared to the Sun, that light would be much redder than sunlight.
This should read: be “much redder than (capital S) Sunlight,” because the light referenced is from our Sun, not just any sun.
Lastly, Mr. Bochanski writes:
“So while our new planetary neighbor may have a dim ….”
The reference to “our new planetary neighbor” is general in a mushy sort of way. That phrasing fits the as-yet-unseen 9th planet in our Solar System, but it is less suitable referring to something which is a planet on the 12th star out away from us.
S&T is extremely valuable. It deserves quality writing.
You must be logged in to post a comment.
November 20, 2017 at 2:51 pm
I'm afraid you changed one of the quotes you're referencing. The correct quote is "This zone, defined as the region in which water could exist in liquid form on a rocky planet’s surface, hugs its star more tightly than it would in the solar system because of the star’s low luminosity." (emphasis added is mine) You abbreviated the quote and added "(Ross 128)", but that's not how it was written in the text — the sentence is referencing the habitable zone, not the planet, and the habitable zone is indeed dependent on the star's luminosity.
Also, according to S&T's style (which we adopt for consistency across the website and magazine), we do capitalize Sun, but we do not capitalize sunlight. Likewise, we capitalize Earth but not earthbound.
You must be logged in to post a comment.
November 18, 2017 at 12:57 pm
We are not alone. Oh, there may not be another planet in all the Universe that has trees and grass and "Beings" on it, but that fact does not necessarily mean that we are alone. Jesus of Nazareth told his friend Peter that he had 20 legions of angelic beings (>1,000,000) that could be brought to his defense if He chose. Considering that we are also told that fully one third of the angelic beings fell from the Heavens, we can assume there is at least another 10 legions of fallen angels or demons. The total of both the Angelic and the fallen being is probably much higher as these numbers here are based on the number being immediately available for a single purpose - I would think the numbers would be measured in Billions or Trillions rather than millions.
The number is not important - the fact that they are there is important because we also know that if we are individually allied with the God of the Universe, then God, and you become the majority stakeholder in the universe and time.
A potentially habitable world, termed Ross 128 b, has been discovered just 11 light years away. It is roughly Earth-sized and orbits its parent star once every 9.9 days. The astronomers reported the discovery in Astronomy and Astrophysics.
That's what I was thinking. Has to be awful close to have that short of an orbit right?
Only 11 light years away you say for sense of distance, the farthest humans have strayed from Earth is
1.3 light seconds. We have hurled an object 140AU (1AU =
500 light seconds) or 19 light hours, Voyager 1 was launched 1977-09-05.
Yes, but even a journey of 10,000-100,000 years isn't impossible with the right motivation and the right technology.
Ah, but this is Ross 128 b.
So with our fastest moving invention to date, how long would it take something to get there? 11 light years seems really close (outer space wise).
You made me Google, so I will share. It would take about 37,200 years for a current space shuttle to go just one light year. Multiply that by 11 and it's a hell of a lot further than I (and likely you) originally thought.
Kinda sad. I want to meet an alien.
11ly is about 1.04x10 14 km. Voyager I (maybe not the fastest) travels at 17km/s. So about. 6.1x10 12 seconds, so almost 194k years. So awhile.
Edit: The fastest was Helios 2, which reached 241350km/h, so about 67 km/s. Piggy backing on this machine will get you to this star 4 times quicker, compared to voyager.
Kinetic energy is 0.5 x mass x velocity 2
So to double velocity takes four times the energy. The most energy we can carry with us with current technology is in highly enriched Uranium or in a breeder reactor, which is 80 TJ/kg. If converted to kinetic energy with perfect efficiency, you could reach 12,650 km/s (4.2% of the speed of light) for the fuel alone.
That does not consider the mass of the rest of the reactor, engine, propellant, or payload. Whatever the ratio of those items are to the nuclear fuel, they slow down what you can reach, because they need to absorb the same kinetic energy as the fuel.
If your energy comes from outside the vehicle, this limit goes away. For example, a modern space solar panel has a power/mass of 180 W/kg, and lasts about 15 years. So it will generate 85 GJ/kg, which is much lower than raw nuclear fuel, but also doesn't need a reactor. The energy can be used directly to power an engine.
The 180 W/kg is for natural sunlight at the Earth's distance from the Sun. If we use concentrated laser power matched to the cell's best frequency, and reprocess the cells when they degrade, we may be able to improve the lifetime output by a factor of 1000, making it even with raw Uranium. So again we reach a number of
At that speed, it will take 275 years to reach Ross 128. Since technology improves faster than that, "inventions to date" is not the right question. It is likely we will come up with something better before we try to travel at that speed.
approximately 66 trillion miles
Who cares about our fastest invention, we have ideas for better propulsion.
Frankly we need to be using lasers to propel craft and we need to get fusion rockets.
X. Bonfils, N. Astudillo-Defru, R. Diaz, J.-M. Almenara, T. Forveille, F. Bouchy, X. Delfosse, C. Lovis, M. Mayor, F. Murgas, F. Pepe, N. C. Santos, D. Segransan, S. Udry, A. Wunsche.
Invite Ross 128 Over This Thanksgiving
By: Bob King November 22, 2017 12
Get Articles like this sent to your inbox
With exoplanet Ross 128b in the news, we pay a visit to the star that sustains this potentially habitable exoplanet.
The red dwarf, Ross 128, hosts the temperate, Earth-sized planet Ross 128 b. The star is about 20% of the Sun's diameter and 17% as massive.
Sloan Digital Sky Survey
No matter where you look the fecundity of the universe is manifest. Consider exoplanets. Since the first was discovered in 1992, astronomers have been piling them on like mashed potatoes at Thanksgiving. Today we know of more than 3,700. Of those, 53 may be potentially habitable.
The most recently discovered potentially life-friendly planet — and in some ways the most exciting — is Ross 128b, which circles the red dwarf star Ross 128 in the constellation Virgo. Located just 11 light-years away, it's the second closest Earth-sized planet within the habitable zone of its star.
Astronomers estimate that temperatures on Ross 128b range from –76° to 68° F (–60° to 20° C). You could argue that's even more temperate than than that of Earth and likely warm enough for liquid water to pool on its surface. What's more, its star experiences far fewer massive flares compared to other red dwarfs, making conditions more hospitable to potential life.
If you have a 4.5-inch or larger telescope, you can track down Ross 128 in Virgo in the morning sky. Place Beta (β) Virginis in the field of a low-power eyepiece and you're halfway there! Mars's location is shown for November 21st.
While you and I aren't going to see Ross 128b anytime soon, we can have the pleasure of seeing its host sun, Ross 128. Currently visible in a dark sky before the start of dawn, this newsy red dwarf is just 1.1° southwest of 3rd-magnitude Beta (β) Virginis. To find the dwarf and its mind's-eye planet, center Beta in the field of view and use the AAVSO map to star-hop right to it.
Once Beta (β) Vir is in the field of view, use this chart from the American Association. of Variable Star Observers to star-hop to Ross 128, also known as the variable star FI Virginis. Numbers are stellar magnitudes with the decimals omitted, so 107 = 10.7. North is up.
AAVSO with annotations by the author
Eager to see it for myself, I got up the first clear morning after the news of the discovery broke last week. Oh gosh, how easy could it be. Pale red and magnitude 11.2, Ross 128 is bright enough to spot in telescopes as small as 4 inches (10 cm). Mingled in the star's light were photons from its closely orbiting and perhaps habitable planet, a satisfying thought.
Some 80% of the Milky Way's stars are red dwarfs, yet not a single one is visible to the naked eye. Being something of an introvert, I cotton to these shy suns. The brightest, Lacaille 8760 in Microscopium, shines at magnitude 6.7. Despite their retiring nature, they make for fertile exoplanet hunting grounds. A tiny dwarf feels a much stronger — and more easily measurable — tug by an orbiting planet compared to a bigger star like our Sun.
This graph shows how the distances of several nearby stars change over a period from 20,000 years in the past to 80,000 years in the future. “0” is the current time distances are given in light years. Ross 128 is closing in, as is Alpha Centauri. Around the year 25,000 AD, the Alpha Centauri system will be just 3 light-years from Earth.
FrancescoA / CC SA-3.0
If we're patient and smart enough not to destroy ourselves, we'll have an even better view of Ross 128 in due time. The star is moving towards us at 31 km/sec and will become our nearest stellar neighbor around 81,000 AD, when only 6.2 light-years will separate the two Earths.
We celebrate Thanksgiving this week, a time to be grateful for all we have. As we reflect on the ups and downs that sustain our lives, feel free to take another helping at the table, including this stellar cranberry.
There’s a new planet in the neighborhood — and it looks like a nice place to live
One of our closest celestial neighbors is a warm, rocky world, scientists say.
Writing in the journal Astronomy and Astrophysics, scientists report the discovery of an Earth-size exoplanet orbiting the star Ross 128, a dim red dwarf just 11 light-years away.
The newfound world, dubbed Ross 128 b, is the closest temperate planet known to orbit a “quiet star” — one that isn't prone to devastating and potentially life-obliterating bursts of radiation.
And it appears to meet some of the basic requirements for habitability. The planet is slightly more massive than Earth, so it is probably a rocky world with a solid surface. The host star is much cooler and fainter than our sun, but Ross 128 b orbits it closely and quickly — a year lasts just 9.9 days. The planet receives about 38 percent more radiation than Earth does — enough to give it an equilibrium temperature between -76 and 68 degrees Fahrenheit, assuming it has an Earthlike atmosphere (and that's a huge assumption).
Though the study authors call Ross 128 b a “temperate planet,” it's not clear whether it falls within the habitable zone — the Goldilocks region where a planet is just warm enough for liquid water to exist on its surface.
Additionally, no current telescopes are capable of analyzing the wavelengths of light coming from the planet, which might provide clues about the existence of an atmosphere and the potential for life. But when the powerful 39-meter Extremely Large Telescope comes online in 2024, this world will be one of its first targets.
Ross 128 b is not Earth's nearest extrasolar neighbor. The exoplanet Proxima b, which orbits the star next door to our sun, is even closer than Ross 128 b — just 4.2 light-years away. But its host star, a red dwarf called Proxima Centauri, has been compared to a hormonal teenager. It produces violent flares of radiation that can strip away an atmosphere and sterilize a planet. You would not be a happy camper if you lived in the vicinity.
Ross 128 is more like a 30-something with a good job, a membership in a yoga studio and an extensive collection of James Taylor albums. You could probably trust it not to fry its own planet.
Indeed, Ross 128 is so agreeable that it's actually heading toward us. According to Nicola Astudillo-Defru, an astronomer at the University of Geneva and co-author of the study, the star's orbit through the galaxy has put it on a path toward Earth. In 71,000 years, it will become our closest neighbor, and Ross 128 will be the closest temperate planet.
Ross 128 b was detected via the High Accuracy Radial velocity Planet Searcher (HARPS), a planet-seeking program based at La Silla Observatory in Chile. As most exoplanets are too distant and too dim to be seen directly, HARPS looks for the telltale signature of a small world orbiting a star. Remember, a planet doesn't really orbit its sun. Rather, both the planet and the sun orbit their common center of mass — the point at which the gravitational forces they exert on each other are at equilibrium. Since stars are so much heftier than planets, that center of mass is a whole lot closer to the star than to the planet, but it is not exactly in the star's middle. This produces a characteristic “wobble.”
All this wobbling affects the radiation these stars emit: The light changes frequency, much the way a sound changes pitch when its source is moving — a phenomenon known as the Doppler Effect.
What if you do spot an alien signal?
Let’s return to the signal from Ross 128. What if the astronomers at Arecibo rule out solar flares and artificial satellites as the origin of the signal? The problem is, we can only rule out the things we know about. So even if these possibilities are discounted, there may still be other causes that have not been thought of yet. In fact, this is how all science works. We can’t ever claim anything is definitely true, we can only rule out the things that are false and make a hypothesis that something else is true until proved otherwise.
But that doesn’t mean that we can’t one day receive a signal that is unambiguously of alien origin. If a signal is received with such a high level of structured information that it can’t be a natural signal, then there may be no other explanation.
In this case, the Search for Extra Terrestrial Intelligence (SETI), have clear protocols for what happens next. These specify that the discoverer must notify other signatories to the protocols, other astronomers around the world, and also the United Nations. All data surrounding the discovery must also be made public. Importantly, no response to the signal should be sent until international consultations have taken place. Whatever (if anything) is transmitted back in the direction the signal came from would indicate our presence, so we’d better be sure we want to announce our existence before doing so.
Maybe one day these protocols will be invoked, but until then, astronomers will keep looking for more prosaic explanations for all the weird signals they detect.