How many exoplanets are there? Not that long ago, we didn’t know if there were any. Then we detected a few around pulsars. Then the Kepler spacecraft was launched and it discovered a couple thousand more. Now NASA’s TESS (Transiting Exoplanet Survey Satellite) is operational, and a new study predicts its findings.
In the past few decades, thousands of extra-solar planets have been discovered within our galaxy. As of July 28th, 2018, a total of 3,374 extra-solar planets have been confirmed in 2,814 planetary systems. While the majority of these planets have been gas giants, an increasing number have been terrestrial (i.e. rocky) in nature and were found to be orbiting within their stars’ respective habitable zones (HZ).
However, as the case of the Solar System shows, HZs do not necessary mean a planet can support life. Even though Venus and Mars are at the inner and the outer edge of the Sun’s HZ (respectively), neither is capable of supporting life on its surface. And with more potentially-habitable planets being discovered all the time, a new study suggests that it might be time to refine our definition of habitable zones.
The study, titled “A more comprehensive habitable zone for finding life on other planets“, recently appeared online. The study was conducted by Dr. Ramses M. Ramirez, a research scientist with the Earth-Life Science Institute at the Tokyo Institute of Technology. For years, Dr. Ramirez has been involved in the study of potentially-habitable worlds and built climate models to assess the processes that make planets habitable.
As Dr. Ramirez indicated in his study, the most generic definition of a habitable zone is the circular region around a star where surface temperatures on an orbiting body would be sufficient to maintain water in a liquid state. However, this alone does not mean a planet is habitable, and additional considerations need to be taken into account to determine if life could truly exist there. As Dr. Ramirez told Universe Today via email:
“The most popular incarnation of the HZ is the classical HZ. This classical definition assumes that the most important greenhouse gases in potentially habitable planets are carbon dioxide and water vapor. It also assumes that habitability on such planets is sustained by the carbonate-silicate cycle, as is the case for the Earth. On our planet, the carbonate-silicate cycle is powered by plate tectonics.
“The carbonate-silicate cycle regulates the transfer of carbon dioxide between the atmosphere, surface, and interior of the Earth. It acts as a planetary thermostat over long timescales and ensures that there is not too much CO2 in the atmosphere (the planet gets too hot) or too little (the planet gets too cold). The classical HZ also (typically) assumes that habitable planets possess total water inventories (e.g. total water in the oceans and seas) similar in size to that on the Earth.”
This is what can be referred to as the “low-hanging fruit” approach, where scientists have looked for signs of habitability based on what we as humans are most familiar with. Given that the only example we have of habitability is planet Earth, exoplanet studies have been focused on finding planets that are “Earth-like” in composition (i.e. rocky), orbit, and size.
However, in recent years this definition has come to be challenged by newer studies. As exoplanet research has moved away from merely detecting and confirming the existence of bodies around other stars and moved into characterization, newer formulations of HZs have emerged that have attempted to capture the diversity of potentially-habitable worlds.
As Dr. Ramirez explained, these newer formulations have complimented traditional notions of HZs by considering that habitable planets may have different atmospheric compositions:
“For instance, they consider the influence of additional greenhouses gases, like CH4 and H2, both of which have been considered important for early conditions on both Earth and Mars. The addition of these gases makes the habitable zone wider than what would be predicted by the classical HZ definition. This is great, because planets thought to be outside the HZ, like TRAPPIST-1h, may now be within it. It has also been argued that planets with dense CO2-CH4 atmospheres near the outer edge of the HZ of hotter stars may be inhabited because it is hard to sustain such atmospheres without the presence of life.”
One such study was conducted by Dr. Ramirez and Lisa Kaltenegger, an associate professor with the Carl Sagan Institute at Cornell University. According to a paper they produced in 2017, which appeared in the Astrophysical Journal Letters, exoplanet-hunters could find planets that would one day become habitable based on the presence of volcanic activity – which would be discernible through the presence of hydrogen gas (H2) in their atmospheres.
This theory is a natural extension of the search for “Earth-like” conditions, which considers that Earth’s atmosphere was not always as it is today. Basically, planetary scientists theorize that billions of years ago, Earth’s early atmosphere had an abundant supply of hydrogen gas (H2) due to volcanic outgassing and interaction between hydrogen and nitrogen molecules in this atmosphere is what kept the Earth warm long enough for life to develop.
In Earth’s case, this hydrogen eventually escaped into space, which is believed to be the case for all terrestrial planets. However, on a planet where there is sufficient levels of volcanic activity, the presence of hydrogen gas in the atmosphere could be maintained, thus allowing for a greenhouse effect that would keep their surfaces warm. In this respect, the presence of hydrogen gas in a planet’s atmosphere could extend a star’s HZ.
According to Ramirez, there is also the factor of time, which is not typically taken into account when assessing HZs. In short, stars evolve over time and put out varying levels of radiation based on their age. This has the effect of altering where a star’s HZ reaches, which may not encompass a planet that is currently being studied. As Ramirez explained:
“[I]t has been shown that M-dwarfs (really cool stars) are so bright and hot when they first form that they can desiccate any young planets that are later determined to be in the classical HZ. This underscores the point that just because a planet is currently located in the habitable zone, it doesn’t mean that it is actually habitable (let alone inhabited). We should be able to watch out for these cases.
Finally, there is the issue of what kinds of star system astronomers have been observing in the hunt for exoplanets. Whereas many surveys have examined G-type yellow dwarf star (which is what our Sun is), much research has been focused on M-type (red dwarf) stars of late because of their longevity and the fact that they believed to be the most likely place to find rocky planets that orbit within their stars’ HZs.
“Whereas most previous studies have focused on single star systems, recent work suggests that habitable planets may be found in binary star systems or even red giant or white dwarf systems, potentially habitable planets may also take the form of desert worlds or even ocean worlds that are much wetter than the Earth,” says Ramirez. “Such formulations not only greatly expand the parameter space of potentially habitable planets to search for, but they allow us to filter out the worlds that are most (and least) likely to host life.”
In the end, this study shows that the classical HZ is not the only tool that can be used to asses the possibility of extra-terrestrial life. As such, Ramirez recommends that in the future, astronomers and exoplanet-hunters should supplement the classical HZ with the additional considerations raised by these newer formulations. In so doing, they just may be able to maximize their chances for finding life someday.
“I recommend that scientists pay real special attention to the early stages of planetary systems because that helps determine the likelihood that a planet that is currently located in the present day habitable zone is actually worth studying further for more evidence of life,” he said. “I also recommend that the various HZ definitions are used in conjunction so that we can best determine which planets are most likely to host life. That way we can rank these planets and determine which ones to spend most of our telescope time and energy on. Along the way we would also be testing how valid the HZ concept is, including determining how universal the carbonate-silicate cycle is on a cosmic scale.”
Further Reading: arXiv
Shortly after Einstein published his Theory of General Relativity in 1915, physicists began to speculate about the existence of black holes. These regions of space-time from which nothing (not even light) can escape are what naturally occur at the end of most massive stars’ life cycle. While black holes are generally thought to be voracious eaters, some physicists have wondered if they could also support planetary systems of their own.
Looking to address this question, Dr. Sean Raymond – an American physicist currently at the University of Bourdeaux – created a hypothetical planetary system where a black hole lies at the center. Based on a series of gravitational calculations, he determined that a black hole would be capable of keeping nine individual Suns in a stable orbit around it, which would be able to support 550 planets within a habitable zone.
He named this hypothetical system “The Black Hole Ultimate Solar System“, which consists of a non-spinning black hole that is 1 million times as massive as the Sun. That is roughly one-quarter the mass of Sagittarius A*, the super-massive black hole (SMBH) that resides at the center of the Milky Way Galaxy (which contains 4.31 million Solar Masses).
As Raymond indicates, one of the immediate advantages of having this black hole at the center of a system is that it can support a large number of Suns. For the sake of his system, Raymond chose 9, thought he indicates that many more could be sustained thanks to the sheer gravitational influence of the central black hole. As he wrote on his website:
“Given how massive the black hole is, one ring could hold up to 75 Suns! But that would move the habitable zone outward pretty far and I don’t want the system to get too spread out. So I’ll use 9 Suns in the ring, which moves everything out by a factor of 3. Let’s put the ring at 0.5 AU, well outside the innermost stable circular orbit (at about 0.02 AU) but well inside the habitable zone (from about 2.7 to 5.4 AU).”
Another major advantage of having a black hole at the center of a system is that it shrinks what is known as the “Hill radius” (aka. Hill sphere, or Roche sphere). This is essentially the region around a planet where its gravity is dominant over that of the star it orbits, and can therefore attract satellites. According to Raymond, a planet’s Hill radius would be 100 times smaller around a million-sun black hole than around the Sun.
This means that a given region of space could stably fit 100 times more planets if they orbited a black hole instead of the Sun. As he explained:
“Planets can be super close to each other because the black hole’s gravity is so strong! If planets are little toy Hot wheels cars, most planetary systems are laid out like normal highways (side note: I love Hot wheels). Each car stays in its own lane, but the cars are much much smaller than the distance between them. Around a black hole, planetary systems can be shrunk way down to Hot wheels-sized tracks. The Hot wheels cars — our planets — don’t change at all, but they can remain stable while being much closer together. They don’t touch (that would not be stable), they are just closer together.”
This is what allows for many planets to be placed with the system’s habitable zone. Based on the Earth’s Hill radius, Raymond estimates that about six Earth-mass planets could fit into stable orbits within the same zone around our Sun. This is based on the fact that Earth-mass planets could be spaced roughly 0.1 AU from each other and maintain a stable orbit.
Given that the Sun’s habitable zone corresponds roughly to the distances between Venus and Mars – which are 0.3 and 0.5 AU away, respectively – this means there is 0.8 AUs of room to work with. However, around a black hole with 1 million Solar Masses, the closest neighboring planet could be just 1/1000th (0.001) of an AU away and still have a stable orbit.
Doing the math, this means that roughly 550 Earths could fit in the same region orbiting the black hole and its nine Suns. There is one minor drawback to this whole scenario, which is that the black hole would have to remain at its current mass. If it were to become any larger, it would cause the Hill radii of its 550 planets to shrink down further and further.
Once the Hill radius got down to the point where it was the same size as any of the Earth-mass planets, the black hole would begin to tear them apart. But at 1 million Solar masses, the black hole is capable of supporting a massive system of planets comfortably. “With our million-Sun black hole the Earth’s Hill radius (on its current orbit) would already be down to the limit, just a bit more than twice Earth’s actual radius,” he says.
Lastly, Raymond considers the implications that living in such a system would have. For one, a year on any planet within the system’s habitable zone would be much shorter, owing to the fact their orbital periods would be much faster. Basically, a year would last roughly 1.6 days for planets at the inner edge of the habitable zone and 4.6 days for planets at the outer edge of the habitable zone.
In addition, on the surface of any planet in the system, the sky would be a lot more crowded! With so many planets in close orbit together, they would pass very close to one another. That essentially means that from the surface of any individual Earth, people would be able to see nearby Earths as clear as we see the Moon on some days. As Raymond illustrated:
“At closest approach (conjunction) the distance between planets is about twice the Earth-Moon distance. These planets are all Earth-sized, about 4 times larger than the Moon. This means that at conjunction each planet’s closest neighbor appears about twice the size of the full Moon in the sky. And there are two nearest neighbors, the inner and outer one. Plus, the next-nearest neighbors are twice as far away so they are still as big as the full Moon during conjunction. And four more planets that would be at least half the full Moon in size during conjunction.”
He also indicates that conjunctions would occur almost once per orbit, which would mean that every few days, there would be no shortage of giant objects passing across the sky. And of course, there would be the Sun’s themselves. Recall that scene in Star Wars where a young Luke Skywalker is watching two suns set in the desert? Well, it would a little like that, except way more cool!
According to Raymond’s calculations, the nine Suns would complete an orbit around the black hole every three hours. Every twenty minutes, one of these Suns would pass behind the black hole, taking just 49 seconds to do so. At this point, gravitational lensing would occur, where the black hole would focus the Sun’s light toward the planet and distort the apparent shape of the Sun.
To illustrate what this would look like, he provides an animation (shown above) created by @GregroxMun – a planet modeller who develops space graphics for Kerbal and other programs – using Space Engine.
While such a system may never occur in nature, it is interesting to know that such a system would be physically possible. And who knows? Perhaps a sufficiently advanced species, with the ability to tow stars and planets from one system and place them in orbit around a black hole, could fashion this Ultimate Solar System. Something for SETI researchers to be on the lookout for, perhaps?
This hypothetical exercise was the second installment in two-part series by Raymond, titled “Black holes and planets”. In the first installment, “The Black Hole Solar System“, Raymond considered what it would be like if our system orbited around a black hole-Sun binary. As he indicated, the consequences for Earth and the other Solar planets would be interesting, to say the least!
Further Reading: PlanetPlanet
Red dwarf stars have become a major focal point for exoplanet studies lately, and for good reason. For starters, M-type (red dwarf) stars are the most common type in our Universe, accounting for 75% of stars in the Milky Way alone. In addition, in the past decade, numerous terrestrial (i.e rocky) exoplanets have been discovered orbiting red dwarf stars, and within their circumstellar habitable zones (“Goldilocks Zones”) to boot.
This has naturally prompted several studies to determine whether or not rocky planets can retain their atmospheres. The latest study comes from NASA, using data obtained by the Mars Atmosphere and Volatile Evolution (MAVEN) orbiter. Having studied Mars’ atmosphere for years to determine how and when it was stripped away, the MAVEN mission is well-suited when it comes to measuring the potential habitability of other planets.
The study was shared on Dec. 13th, 2017, at the Fall Meeting of the American Geophysical Union in New Orleans, Louisiana. In a presentation titled “Spanning Disciplines to Search for Life Beyond Earth“, a team of NASA scientists and researchers from the University of California-Riverside and the University of Colorado-Boulder explained how insights from the MAVEN mission could be applied to the habitability of rocky planets orbiting other stars.
Launched in November 18th, 2013, the MAVEN mission established orbit around Mars on September 22nd, 2014. The purpose of this mission has been to explore the Red Planet’s upper atmosphere, ionosphere and its interactions with the Sun and solar wind for the sake of determining how and when Mars’ atmosphere went from being thicker and warmer in the past (and thus able to support liquid water on the surface) to thin and tenuous today.
Since November of 2014, MAVEN has been measuring Mars’ atmospheric loss using its suite of scientific instruments. From the data it has obtained, scientists have surmised that the majority of the planet’s atmosphere was lost to space over time due to a combination of chemical and physical processes. And in the past three years, the Sun’s activity has increased and decreased, giving MAVEN the opportunity to observe how Mars’ atmospheric loss has risen and fallen accordingly.
Because of this, David Brain – a professor at the Laboratory for Atmospheric and Space Physics (LASP) at the CU Boulder is also a MAVEN co-investigator – and his colleagues began to think about how these insights could be applied to a hypothetical Mars-like planet orbiting around an red dwarf star. These planets include Proxima b (the closest exoplanet to our Solar System) and the seven planet system of TRAPPIST-1.
As Brain he explained in a recent NASA press release:
“The MAVEN mission tells us that Mars lost substantial amounts of its atmosphere over time, changing the planet’s habitability. We can use Mars, a planet that we know a lot about, as a laboratory for studying rocky planets outside our solar system, which we don’t know much about yet.”
To determine if this hypothetical planet could retain its atmosphere over time, the researchers performed some preliminary calculations that assumed that this planet would be positioned near the outer edge of the star’s habitable zone (as Mars is). Since red dwarf’s are dimmer than our Sun, the planet would have to orbit much closer to the star – even closer than Mercury does to our Sun – to be within this zone.
They also considered how a higher proportion of the light emanating from red dwarf stars is in the ultraviolet wavelength. Combined with a close orbit, this means that the hypothetical planet would be bombarded with about 5 times more UV radiation the real Mars gets. This would also mean that the processes responsible for atmospheric loss would be increased for this planet.
Based on data obtained by MAVEN, Brain and colleagues were able to estimate how this increase in radiation would affect Mars’ own atmospheric loss. Based on their calculations, they found that the planet’s atmosphere would lose 3 to 5 times as many charged particles through ion escape, while about 5 to 10 times more neutral particles would be lost through photochemical escape (where UV radiaion breaks apart molecules in the upper atmosphere).
Another form of atmospheric loss would also result, due to the fact that more UV radiation means that more charged particles would be created. This would result in a process called “sputtering”, where energetic particles are accelerated into the atmosphere and collide with other molecules, kicking some out into space and sending others crashing into neighboring particles.
Lastly, they considered how the hypothetical planet might experience about the same amount of thermal escape (aka. Jeans escape) as the real Mars. This process occurs only for lighter molecules such as hydrogen, which Mars loses at the top of its atmosphere through thermal escape. On the “exo-Mars”, however, thermal escape would increase only if the increase in UV radiation were to push more hydrogen into the upper atmosphere.
In conclusion, the researchers determined that orbiting at the edge of the habitable zone of a quiet M-type star (instead of our Sun) could shorten the habitable period for a Mars-like planet by a factor of about 5 to 20. For a more active M-type star, the habitable period could be cut by as much as 1,000 times. In addition, solar storm activity around a red dwarf, which is thousands of times more intense than with our Sun, would also be very limiting.
However, the study is based on how an exo-Mars would fair around and M-type star, which kind of stacks the odds against habitability in advance. When different planets are considered, which possess mitigating factors Mars does not, things become a bit more promising. For instance, a planet that is more geologically active than Mars would be able to replenish its atmosphere at a greater rate.
Other factors include increase mass, which would allow for the planet to hold onto more of its atmosphere, and the presence of a magnetic field to shield it from stellar wind. As Bruce Jakosky, MAVEN’s principal investigator at the University of Colorado (who was not associated with this study), remarked:
“Habitability is one of the biggest topics in astronomy, and these estimates demonstrate one way to leverage what we know about Mars and the Sun to help determine the factors that control whether planets in other systems might be suitable for life.”
In the coming years, astronomers and exoplanet researchers hope to learn more about the planets orbiting nearby red dwarf stars. These efforts are expected to be helped immensely thanks to the deployment of the James Webb Space Telescope, which will be able to conduct more detailed surveys of these star systems using its advanced infrared imaging capabilities.
These studies will allow scientists to place more accurate constraints on exoplanets that orbit red dwarf stars, which will allow for better estimates about their size, mass, and compositions – all of which are crucial to determining potential habitability.
In February of 2017, a team of European astronomers announced the discovery of a seven-planet system orbiting the nearby star TRAPPIST-1. Aside from the fact that all seven planets were rocky, there was the added bonus of three of them orbiting within TRAPPIST-1’s habitable zone. As such, multiple studies have been conducted that have sought to determine whether or not any planets in the system could be habitable.
When it comes to habitability studies, one of the key factors to consider is the age of the star system. Basically, young stars have a tendency to flare up and release harmful bursts of radiation while planets that orbit older stars have been subject to radiation for longer periods of time. Thanks to a new study by a pair of astronomers, it is now known that the TRAPPIST-1 system is twice as old as the Solar System.
The study, which will be published in The Astrophysical Journal under the title “On The Age Of The TRAPPIST-1 System“, was led by Adam Burgasser, an astronomer at the University of California San Diego (UCSD). He was joined by Eric Mamajek, the deputy program scientist for NASA’s Exoplanet Exploration Program (EEP) at the Jet Propulsion Laboratory.
Together, they consulted data on TRAPPIST-1s kinematics (i.e. the speed at which it orbits the center of the galaxy), its age, magnetic activity, density, absorption lines, surface gravity, metallicity, and the rate at which it experiences stellar flares. From all this, they determined that TRAPPIST-1 is quite old, somewhere between 5.4 and 9.8 billion years of age. This is up to twice as old as our own Solar System, which formed some 4.5 billion years ago.
These results contradict previously-held estimates, which were that the TRAPPIST-1 system was about 500 millions yeas old. This was based on the fact that it would have taken this long for a low-mass star like TRAPPIST-1 (which has roughly 8% the mass of our Sun) to contract to its minimum size. But with an upper age limit that is just under 10 billion years, this star system could be almost as old as the Universe itself!
As Dr. Burgasser explained in a recent NASA press statement:
“Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago.”
The implications of this could be very significant as far as habitability studies are concerned. For one, older stars experience less in the way of flareups compared to younger ones. From their study, Burgasser and Mamajek confirmed that TRAPPIST-1 is relatively quiet compared to other ultra-cool dwarf stars. However, since the planets around TRAPPIST-1 orbit so close to their star, they have been exposed to billions of years of radiation at this point.
As such, it is possible that most of the planets which orbit TRAPPIST-1 – expect for the outermost two, g and h – would probably have had their atmospheres stripped away – similar to what happened to Mars billions of years ago when it lost its protective magnetic field. This is certainly consistent with many recent studies, which concluded that TRAPPIST-1’s solar activity would not be conducive to life on any of its planets.
Whereas some of these studies addressed TRAPPIST-1s level of stellar flare, others examined the role magnetic fields would play. In the end, they concluded that TRAPPIST-1 was too variable, and that its own magnetic field would likely be connected to the fields of its planets, allowing particles from the star to flow directly onto the planets atmospheres (thus allowing them to be more easily stripped away).
However, the results were not entirely bad news. Since the TRAPPIST-1 planets have estimated densities that are lower than that of Earth, it is possible that they have large amounts of volatile elements (i.e. water, carbon dioxide, ammonia, methane, etc). These could have led to the formation of thick atmospheres that protected the surfaces from a lot of harmful radiation and redistributed heat across the tidally-locked planets.
Then again, a thick atmosphere could also have an effect akin to Venus, creating a runaway greenhouse effect that would have resulted in incredibly thick atmospheres and extremely hot surfaces. Under the circumstances, then, any life that emerged on these planets would have had to be extremely hardy in order to survive for billions of years.
Another positive thing to consider is TRAPPIST-1’s constant brightness and temperature, which are also typical of M-class (red dwarf) stars. Stars like our Sun have an estimated lifespan of 10 billion years (which it is almost halfway through) and grow steadily brighter and hotter with time. Red dwarfs, on the other hand, are believed to exist for as much as 10 trillion years – far longer than the Universe has existed – and do not change much in intensity.
Given the amount of time it took for complex life to have emerged on Earth (over 4.5 billion years), this longevity and consistency could make red dwarf star systems the best long-term bet for habitability. Such was the conclusion of one recent study, which was conducted by Prof. Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA). And as Mamajek explained:
“Stars much more massive than the Sun consume their fuel quickly, brightening over millions of years and exploding as supernovae. But TRAPPIST-1 is like a slow-burning candle that will shine for about 900 times longer than the current age of the universe.”
NASA has also expressed excitement over these findings. “These new results provide useful context for future observations of the TRAPPIST-1 planets, which could give us great insight into how planetary atmospheres form and evolve, and persist or not,” said Tiffany Kataria, an exoplanet scientist at JPL. At the moment, habitability studies of TRAPPIST-1 and other nearby star systems are confined to indirect methods.
However, in the near future, next-generation missions like the James Webb Space Telescope are expected to reveal additional information – such as whether or not these planets have atmospheres and what their compositions are. Future observations with the Hubble Space Telescope and the Spitzer Space Telescope are also expected to improve our understanding of these planets and possible conditions on their surface.
You can catch a glimpse of what its like to see NASA’s Curiosity Mars rover simultaneously high overhead from orbit and trundling down low across the Red Planet’s rocky surface as she climbs the breathtaking terrain of Mount Sharp – as seen in new images from NASA we have stitched together into a mosaic view showing the perspective views; see above.
Earlier this month on June 5, researchers commanded NASA’s Mars Reconnaissance Orbiter (MRO) to image the car sized Curiosity rover from Mars orbit using the spacecrafts onboard High Resolution Imaging Science Experiment (HiRISE) telescopic camera during Sol 1717 of her Martian expedition – see below.
HiRISE is the most powerful telescope ever sent to Mars.
And as she does nearly every Sol, or Martian day, Curiosity snapped a batch of new images captured from Mars surface using her navigation camera called navcam – likewise on Sol 1717.
Since NASA just released the high resolution MRO images of Curiosity from orbit, we assembled together the navcam camera raw images taken simultaneously on June 5 (Sol 1717), in order to show the actual vista seen by the six wheeled robot from a surface perspective on the same day.
The lead navcam photo mosaic shows a partial rover selfie backdropped by the distant rim of Gale Crater – and was stitched together by the imaging team of Ken Kremer and Marco Di Lorenzo.
Right now NASA’s Curiosity Mars Science Laboratory (MSL) rover is approaching her next science destination named “Vera Rubin Ridge” while climbing up the lower reaches of Mount Sharp, the humongous mountain that dominates the rover’s landing site inside Gale Crater.
“When the MRO image was taken, Curiosity was partway between its investigation of active sand dunes lower on Mount Sharp, and “Vera Rubin Ridge,” a destination uphill where the rover team intends to examine outcrops where hematite has been identified from Mars orbit,” says NASA.
“HiRISE has been imaging Curiosity about every three months, to monitor the surrounding features for changes such as dune migration or erosion.”
The MRO image has been color enhanced and shows Curiosity as a bright blue feature. It is currently traveling on the northwestern flank of Mount Sharp. Curiosity is approximately 10 feet long and 9 feet wide (3.0 meters by 2.8 meters).
“The exaggerated color, showing differences in Mars surface materials, makes Curiosity appear bluer than it really looks. This helps make differences in Mars surface materials apparent, but does not show natural color as seen by the human eye.”
See our mosaic of “Vera Rubin Ridge” and Mount Sharp below.
Curiosity is making rapid progress towards the hematite-bearing location of Vera Rubin Ridge after conducting in-depth exploration of the Bagnold Dunes earlier this year.
“Vera Rubin Ridge is a high-standing unit that runs parallel to and along the eastern side of the Bagnold Dunes,” says Mark Salvatore, an MSL Participating Scientist and a faculty member at Northern Arizona University, in a new mission update.
“From orbit, Vera Rubin Ridge has been shown to exhibit signatures of hematite, an oxidized iron phase whose presence can help us to better understand the environmental conditions present when this mineral assemblage formed.”
Curiosity will use her cameras and spectrometers to elucidate the origin and nature of Vera Rubin Ridge and potential implications or role in past habitable environments.
“The rover will turn its cameras to Vera Rubin Ridge for another suite of high resolution color images, which will help to characterize any observed layers, fractures, or geologic contacts. These observations will help the science team to determine how Vera Rubin Ridge formed and its relationship to the other geologic units found within Gale Crater.”
To reach Vera Rubin Ridge, Curiosity is driving east-northeast around two small patches of dunes just to the north. She will then turn “southeast and towards the location identified as the safest place for Curiosity to ascend the ridge. Currently, this ridge ascent point is approximately 370 meters away.”
Ascending and diligently exploring the sedimentary lower layers of Mount Sharp, which towers 3.4 miles (5.5 kilometers) into the Martian sky, is the primary destination and goal of the rovers long term scientific expedition on the Red Planet.
“Lower Mount Sharp was chosen as a destination for the Curiosity mission because the layers of the mountain offer exposures of rocks that record environmental conditions from different times in the early history of the Red Planet. Curiosity has found evidence for ancient wet environments that offered conditions favorable for microbial life, if Mars has ever hosted life,” says NASA.
As of today, Sol 1733, June 21, 2017, Curiosity has driven over 10.29 miles (16.57 kilometers) since its August 2012 landing inside Gale Crater, and taken over 420,000 amazing images.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Learn more about the upcoming SpaceX launch of BulgariaSat 1, recent SpaceX Dragon CRS-11 resupply launch to ISS, NASA missions and more at Ken’s upcoming outreach events at Kennedy Space Center Quality Inn, Titusville, FL:
June 22-24: “SpaceX BulgariaSat 1 launch, SpaceX CRS-11 and CRS-10 resupply launches to the ISS, Inmarsat 5 and NRO Spysat, EchoStar 23, SLS, Orion, Commercial crew capsules from Boeing and SpaceX , Heroes and Legends at KSCVC, ULA Atlas/John Glenn Cygnus launch to ISS, SBIRS GEO 3 launch, GOES-R weather satellite launch, OSIRIS-Rex, Juno at Jupiter, InSight Mars lander, SpaceX and Orbital ATK cargo missions to the ISS, ULA Delta 4 Heavy spy satellite, Curiosity and Opportunity explore Mars, Pluto and more,” Kennedy Space Center Quality Inn, Titusville, FL, evenings
M-type stars, also known as “red dwarfs”, have become a popular target for exoplanet hunters of late. This is understandable given the sheer number of terrestrial (i.e. rocky) planets that have been discovered orbiting around red dwarf stars in recent years. These discoveries include the closest exoplanet to our Solar System (Proxima b) and the seven planets discovered around TRAPPIST-1, three of which orbit within the star’s habitable zone.
The latest find comes from a team of international astronomers who discovered a planet around GJ 625, a red dwarf star located just 21 light years away from Earth. This terrestrial planet is roughly 2.82 times the mass of Earth (aka. a “super-Earth”) and orbits within the star’s habitable zone. Once again, news of this discovery is prompting questions about whether or not this world could indeed be habitable (and also inhabited).
The international team was led by Alejandro Mascareño of the Canary Islands Institute of Astrophysics (IAC), and includes members from the University of La Laguna and the University of Geneva. Their research was also supported by the Spanish National Research Council (CSIS), the Institute of Space Studies of Catalonia (IEEC), and the National Institute For Astrophysics (INAF).
The study which details their findings was recently accepted for publication by the journal Astronomy & Astrophysics, and appears online under the title “A super-Earth on the Inner Edge of the Habitable Zone of the Nearby M-dwarf GJ 625“. According to the study, the team used radial-velocity measurements of GJ 625 in order to determine the presence of a planet that has between two and three times the mass of Earth.
This discovery was part of the HArps-n red Dwarf Exoplanet Survey (HADES), which studies red dwarf stars to determine the presence of potentially habitable planets orbiting them. This survey relies on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) instrument – which is part of the 3.6-meter Galileo National Telescope (TNG) at the IAC’s Roque de Los Muchachos Observatory on the island of La Palma.
Using this instrument, the team collected high-resolution spectroscopic data of the GJ 625 system over the course of three years. Specifically, they measured small variations in the stars radial velocity, which are attributed to the gravitational pull of a planet. From a total of 151 spectra obtained, they were able to determine that the planet (GJ 625 b) was likely terrestrial and had a minimum mass of 2.82 ± 0.51 Earth masses.
Moreover, they obtained distance estimates that placed it roughly 0.078 AU from its star, and an orbital period estimate of 14.628 ± 0.013 days. At this distance, the planet’s orbit places it just within GJ 625’s habitable zone. Of course, this does not mean conclusively that the planet has conditions conducive to life on its surface, but it is an encouraging indication.
As Alejandro Suárez Mascareño explained in an IAC press release:
“As GJ 625 is a relatively cool star the planet is situated at the edge of its habitability zone, in which liquid water can exist on its surface. In fact, depending on the cloud cover of its atmosphere and on its rotation, it could potentially be habitable”.
This is not the first time that the HADES project detected an exoplanet around a red dwarf star. In fact, back in 2016, a team of international researchers used this project to discover 2 super-Earths orbiting GJ 3998, a red dwarf located about 58 ± 2.28 light years from Earth. Beyond HADES, this discovery is yet another in a long line of rocky exoplanets that have been discovered in the habitable zone of a nearby red dwarf star.
Such findings are very encouraging since red dwarfs are the most common type of star in the known Universe- accounting for an estimated 70% of stars in our galaxy alone. Combined with the fact that they can exist for up to 10 trillion years, red dwarf systems are considered a prime candidate in the search for habitable exoplanets.
But as with all other planets discovered around red dwarf stars, there are unresolved questions about how the star’s variability and stability could affect the planet. For starters, red dwarf stars are known to vary in brightness and periodically release gigantic flares. In addition, any planet close enough to be within the star’s habitable zone would likely be tidally-locked with it, meaning that one side would be exposed to a considerable amount of radiation.
As such, additional observations will need to be made of this exoplanet candidate using the time-tested transit method. According to Jonay Hernández – a professor from the University of La Laguna, a researcher with the IAC and one of the co-authors on the study – future studies using this method will not only be able to confirm the planet’s existence and characterize it, but also determine if there are any other planets in the system.
“In the future, new observing campaigns of photometric observations will be essential to try to detect the transit of this planet across its star, given its proximity to the Sun,” he said. “There is a possibility that there are more rocky planets around GJ 625 in orbits which are nearer to, or further away from the star, and within the habitability zone, which we will keep on combing”.
According to Rafael Rebolo – one of the study’s co-authors from the Univeristy of La Laguna, a research with the IAC, and a member of the CSIS – future surveys using the transit method will also allow astronomers to determine with a fair degree of certainty whether or not GJ 625 b has the all-important ingredient for habitability – i.e. an atmosphere:
“The detection of a transit will allow us to determine its radius and its density, and will allow us to characterize its atmosphere by the transmitted light observe using high resolution high stability spectrographs on the GTC or on telescopes of the next generation in the northern hemisphere, such as the Thirty Meter Telescope (TMT)”.
But what is perhaps most exciting about this latest find is how it adds to the population of extra-solar planets within our cosmic neighborhood. Given their proximity, each of these planets represent a major opportunity for research. And as Dr. Mascareño told Universe Today via email:
“While we have already found more than 3600 extra-solar planets, the exoplanet population in our near neighborhood is still somewhat unknown. At 21 ly from the Sun, GJ 625 is one of the 100 nearest stars, and right now GJ 625 b is one of the 30 nearest exoplanets detected and the 6th nearest potentially habitable exoplanet.”
Once again, ongoing surveys of nearby star systems is providing plenty of potential targets in the search for life beyond our Solar System. And with both ground-based and space-based next-generation telescopes joining the search, we can expect to find many, many more candidates in the coming years. In the meantime, be sure to check out this animation of GJ 625 b and its parent star:
Back in February of 2017, NASA announced the discovery of a seven-planet system orbiting a nearby star. This system, known as TRAPPIST-1, is of particular interest to astronomers because of the nature and orbits of the planets. Not only are all seven planets terrestrial in nature (i.e. rocky), but three of the seven have been confirmed to be within the star’s habitable zone (aka. “Goldilocks Zone”).
But beyond the chance that some of these planets could be inhabited, there is also the possibility that their proximity to each other could allow for life to be transferred between them. That is the possibility that a team of scientists from the University of Chicago sought to address in a new study. In the end, they concluded that bacteria and single-celled organisms could be hopping from planet to planet.
This study, titled “Fast Litho-panspermia in the Habitable Zone of the TRAPPIST-1 System“, was recently published in the Astrophysical Journal Letters. For the sake of seeing if life could be distributed within this star system (aka. litho-panspermia), Krijt and his fellow UChicago scientists ran simulations that showed that this process could happen 4 to 5 times faster than it would in our Solar System.
As Sebastiaan Krijt – a postdoctoral scholar at UChicago and the lead author on the study – said in a University press release:
“Frequent material exchange between adjacent planets in the tightly packed TRAPPIST-1 system appears likely. If any of those materials contained life, it’s possible they could inoculate another planet with life.”
For the sake of their study, the team considered that any transfers of life would likely involve asteroids or comets striking planets within the star’s habitable zone (HZ) and then transferring the resulting material to other planets. They then simulated the trajectories that the ejecta would take, and tested to see if it would have the necessary speed to get out of orbit (escape velocity) and be captured by a neighboring planet’s gravity.
In the end, they determined that roughly 10% of the material that would be capable of transferring life would have the velocity necessary to not only achieve escape velocity. This covered the pieces of ejecta that would be large enough to endure irradiation and the heat of re-entry. What’s more, they found that this material would be able to reach another HZ planet with periods ranging from 10 to 100 years.
For over a century, scientists have considered the possibility that life may be distributed throughout our Universe by meteoroids, asteroids, comets, and planetoids. Similarly, multiple studies have been conducted to see if the building blocks of life could have come to Earth (and been distributed throughout the Solar System) in the same way.
Every year, an estimated 36,287 metric tons (40,000 tons) of space debris falls to Earth, and material that has been ejected from our planet is floating around out in space as well. And we know for a fact that Earth and Mars have exchanged material on several occasions, where Martian ejecta kicked up by asteroids and comets was thrown into space and eventually collided with our planet.
As such, studies like this can help us to understand how life came to be in our Solar System. At the same time, they can illustrate how in other star systems, the process may be far more intense. As Fred Ciesla – a professor of geophysical sciences at UChicago and a co-author of the paper – explained:
“Given that tightly packed planetary systems are being detected more frequently, this research will make us rethink what we expect to find in terms of habitable planets and the transfer of life—not only in the TRAPPIST-1 system, but elsewhere. We should be thinking in terms of systems of planets as a whole, and how they interact, rather than in terms of individual planets.”
And with all the exoplanets discoveries made of late – which can only be described as explosive – opportunities for research are similarly exploding. In total, some 3,483 exoplanets have been confirmed so far, with an additional 4,496 candidates awaiting confirmation. Of the confirmed planets, 581 have been found to exist within multi-planet systems (like TRAPPIST-1), each of which present the possibility of litho-panspermia.
By studying more and more in the way of distant planets, we can reach beyond our own Solar System to see how planets evolve, interact, and how life can come to exist on them. And someday, we may actually be able to study them up close! One can only imagine what we may find…
On February 22nd, 2017, NASA announced the discovery of a seven-planet system around the red dwarf star known as TRAPPIST-1. Since that time, a number of interesting revelations have been made. For starters, the Search for Extra-Terrestrial Intelligence (SETI) recently announced that it was already monitoring this system for signs of advanced life (sadly, the results were not encouraging).
In their latest news release about this nearby star system, NASA announced the release of the first images taken of this system by the Kepler mission. As humanity’s premier planet-hunting mission, Kepler has been observing this system since December 2016, a few months after the existence of the first three of its exoplanets were announced.
These observations took place between December 15th, 2016 and March 4th, 2017, as part of Kepler’s extended mission (known as K2). During this 74-day period, K2 collected data on minuscule changes in the star’s brightness, which were caused by transits made by the star’s exoplanets. And as of Wednesday, March. 8th, this information is now available to the scientific community.
These observations constituted the longest continuous set of observations of the star system to date. But in truth, the initial coordinates designated for this observation (known as Campaign 12) were set back in Oct. 2015, and did not focus on TRAPPIST-1. But as of May 2016, when the system’s first three planets were announced, the science teams adjusted their focus to observe them.
As Michael Haas, the science office director for the Kepler and K2 missions at NASA’s Ames Research Center, explained:
“We were lucky that the K2 mission was able to observe TRAPPIST-1. The observing field for Campaign 12 was set when the discovery of the first planets orbiting TRAPPIST-1 was announced, and the science community had already submitted proposals for specific targets of interest in that field. The unexpected opportunity to further study the TRAPPIST-1 system was quickly reconized and the agility of the K2 team and science community prevailed once again.”
While the data is raw and uncalibrated, it is expected to help astronomers learn more about this system of planets. In particular, it could help astronomers to place constraints on the seventh planet’s orbital period and mass (which are currently unknown). Additional information about the other six planets, particularly their size and mass, could also help astronomers make more accurate assessments about their composition.
The magnetic activity of the host star, which is important in determining if any of its planets could be habitable, is also something that astronomers would like to learn more about. Last, but not least, the new data will help astronomers to prepare proposals for the use Earth-based telescopes next winter to further investigate TRAPPIST-1.
These proposals are due this month, and the timely arrival of this data ought to help research teams to refine their research objectives for next year. Any refinements made using this data will also help astronomer plan for follow-up studies using next-generations telescopes like the James Webb Space Telescope. As Geert Barentsen, a K2 research scientist at NASA’s Ames Research Center, explained:
“Scientists and enthusiasts around the world are invested in learning everything they can about these Earth-size worlds. Providing the K2 raw data as quickly as possible was a priority to give investigators an early look so they could best define their follow-up research plans. We’re thrilled that this will also allow the public to witness the process of discovery.
By the end of May 2017, the data will be fully processed and calibrated, which will also be made available to the public. As you can see from the images above, it was a little on the pixelated side! Still, we can expect some interesting finds to come out of this crowded star system in the coming months. Hopefully, some of that information will help us to determine if there’s any real chance of life forming there.
The Trappist-1 system has been featured in the news quite a bit lately. In May of 2016, it appeared in the headlines after researchers announced the discovery of three exoplanets orbiting around the red dwarf star. And then there was the news earlier this week of how follow-up examinations from ground-based telescopes and the Spitzer Space Telescope revealed that there were actually seven planets in this system.
And now it seems that there is more news to be had from this star system. As it turns out, the Search for Extraterrestrial Intelligence (SETI) Institute was already monitoring this system with their Allen Telescope Array (ATA), looking for signs of life even before the multi-planet system was announced. And while the survey did not detect any telltale signs of radio traffic, further surveys are expected.
Given its proximity to our own Solar System, and the fact that this system contains seven planets that are similar in size and mass to Earth, it is both tempting and plausible to think that life could be flourishing in the TRAPPIST-1 system. As Seth Shostak, a Senior Astronomer at SETI, explained:
“[T]he opportunities for life in the Trappist 1 system make our own solar system look fourth-rate. And if even a single planet eventually produced technically competent beings, that species could quickly disperse its kind to all the rest… Typical travel time between worlds in the Trappist 1 system, even assuming rockets no speedier than those built by NASA, would be pleasantly short. Our best spacecraft could take you to Mars in 6 months. To shuttle between neighboring Trappist planets would be a weekend junket.”
Little wonder then why SETI has been using their Allen Telescope Array to monitor the system ever since exoplanets were first announced there. Located at the Hat Creek Radio Observatory in northern California (northeast of San Francisco), the ATA is what is known as a “Large Number of Small Dishes” (LNSD) array – which is a new trend in radio astronomy.
Like other LNSD arrays – such as the proposed Square Kilometer Array currently being built in Australia and South Africa – the concept calls for the deployment of many smaller dishes over a large surface area, rather than a single large dish. Plans for the array began back in 1997, when the SETI Institute convened a workshop to discuss the future of the Institute and its search strategies.
The final report of the workshop, titled “SETI 2020“, laid out a plan for the creation of a new telescope array. This array was referred to as the One Hectare Telescope at the time, since the plan called for a LNSD encompassing an area measuring 10,000 m² (one hectare). The SETI Institute began developing the project in conjunction with the Radio Astronomy Laboratory (RAL) at the UC Berkeley.
In 2001, they secured a $11.5 million donation from the Paul G. Allen Family Foundation, which was established by Microsoft co-founder Paul Allen. In 2007, the first phase of construction was completed and the ATA finally became operational on October 11th, 2007, with 42 antennas (ATA-42). Since that time, Allen has committed to an additional $13.5 million in funding for a second phase of expansion (hence why it bears his name).
Compared to large, single dish-arrays, smaller dish-arrays are more cost-effective because they can be upgraded simply by adding more dishes. The ATA is also less expensive since it relies on commercial technology originally developed for the television market, as well as receiver and cryogenic technologies developed for radio communication and cell phones.
It also uses programmable chips and software for signal processing, which allows for rapid integration whenever new technology becomes available. As such, the array is well suited to running simultaneous surveys at centimeter wavelengths. As of 2016, the SETI Institute has performed observations with the ATA for 12 hour periods (from 6 pm and 6 am), seven days a week.
And last year, the array was aimed towards TRAPPIST-1, where it conducted a survey scanning ten billion radio channels in search of signals. Naturally, the idea that a radio signal would be emanating from this system, and one which the ATA could pick up, might seem like a bit of a longshot. But in fact, both the infrastructure and energy requirements would not be beyond a species who’s technical advancement is commensurate with our own.
“Assuming that the putative inhabitants of this solar system can use a transmitting antenna as large as the 500 meter FAST radio telescope in China to beam their messages our way, then the Allen Array could have found a signal if the aliens use a transmitter with 100 kilowatts of power or more,” said Shostak. “This is only about ten times as energetic as the radar down at your local airport.”
So far, nothing has been picked up from this crowded system. But the SETI Institute is not finished and future surveys are already in the works. If there is a thriving, technologically-advanced civilization in this system (and they know their way around a radio antenna), surely there will be signs soon enough.
And regardless, the discovery of seven planets in the TRAPPIST-1 system is very exciting because it demonstrates just how plentiful systems that could support life are in our Universe. Not only does this system have three planets orbiting within its habitable zone (all of which are similar in size and mass to Earth), but the fact that they orbit a red dwarf star is very encouraging.
These stars are the most common in our Universe, making up 70% of stars in our galaxy, and up to 90% in elliptical galaxies. They are also very stable, remaining in their Main Sequence phase for up to 10 trillion years. Last, but not least, astronomers believe that 20 out of 30 nearest stars to our Solar System are red dwarfs. Lots of opportunities to find life within a few dozen light years!
“[W]hether or not Trappist 1 has inhabitants, its discovery has underlined the growing conviction that the Universe is replete with real estate on which biology could both arise and flourish,’ says Shostak. “If you still think the rest of the universe is sterile, you are surely singular, and probably wrong.”
Further Reading: SETI