White Dwarfs Could Support Life. So Where are All Their Planets?

Artist's view of old white dwarfs surrounded by planetary debris. Credit: University of Warwick/Dr Mark Garlick

Astronomers have found plenty of white dwarf stars surrounded by debris disks. Those disks are the remains of planets destroyed by the star as it evolved. But they’ve found one intact Jupiter-mass planet orbiting a white dwarf.

Are there more white dwarf planets? Can terrestrial, Earth-like planets exist around white dwarfs?

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What’s the Best Way to Find Planets in the Habitable Zone?

This artist's illustration of Kepler 22-b, an Earth-like planet in the habitable zone of a Sun-like star about 640 light years (166 parsecs) away. Credit: NASA/Ames/JPL-Caltech

Despite the fact that we’ve discovered thousands of them, exoplanets are hard to find. And some types are harder to find than others. Naturally, some of the hardest ones to find are the ones we most want to find. What can we do?

Keep working on it, and that’s what a trio of Chinese scientists are doing.

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A Rogue Earth and Neptune Might Have Been Found in Older Data

An artist's illustration of a rogue planet, dark and mysterious. Image Credit: NASA

Scientists have found what appear to be rogue planets hidden in old survey data. Their results are starting to define the poorly-understood rogue planet population. In the near future, the Nancy Grace Roman Space Telescope will conduct a search for more free-floating planets, and the team of researchers developed some methods that will aid that search.

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To Take the Best Direct Images of Exoplanets With Space Telescopes, we’re Going to Want Starshades

Between 2021 and 2024, the James Webb (JWST) and Nancy Grace Roman (RST) space telescopes will be launched to space. As the successors to multiple observatories (like Hubble, Kepler, Spitzer, and others), these missions will carry out some of the most ambitious astronomical surveys ever mounted. This will range from the discovery and characterization of extrasolar planets to investigating the mysteries of Dark Matter and Dark Energy.

In addition to advanced imaging capabilities and high sensitivity, both instruments also carry coronagraphs – instruments that suppress obscuring starlight so exoplanets can be detected and observed directly. According to a selection of papers recently published by the Journal of Astronomical Telescopes, Instruments, and Systems (JATIS), we’re going to need more of these instruments if we truly want to really study exoplanets in detail.

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Most Exoplanets won’t Receive Enough Radiation to Support an Earth-Like Biosphere

Earth as seen by the JUNO spacecraft in 2013. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill.

To date, astronomers have confirmed the existence of 4,422 extrasolar planets in 3,280 star systems, with an additional 7,445 candidates awaiting confirmation. Of these, only a small fraction (165) have been terrestrial (aka. rocky) in nature and comparable in size to Earth – i.e., not “Super-Earths.” And even less have been found that are orbiting within their parent star’s circumsolar habitable zone (HZ).

In the coming years, this is likely to change when next-generation instruments (like James Webb) are able to observe smaller planets that orbit closer to their stars (which is where Earth-like planets are more likely to reside). However, according to a new study by researchers from the University of Napoli and the Italian National Institute of Astrophysics (INAF), Earth-like biospheres may be very rare for exoplanets.

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Some Stars Could Support as Many as 7 Habitable Planets

Most exoplanets orbit red dwarf stars because they're the most plentiful stars. This is an artist's illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech
Most exoplanets orbit red dwarf stars because they're the most plentiful stars. This is an artist's illustration of what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credits: NASA/JPL-Caltech

In recent decades, over 4,000 extrasolar planets have been confirmed beyond our Solar System. With so many planets available for study, astronomers have learned a great deal about the types of planets that exist out there and what kind of conditions are prevalent. For instance, they have been able to get a better idea of just how common habitable planets are (at least by our standards).

As it turns out, a surprisingly high number of planets out there could support life. That is the conclusion reached by a team of astronomers and planetary scientists who conducted a study of the possible sizes of habitable zones (HZ) based on stellar classification. After considering many planets could stably orbit within them, they came to the conclusion that stars with no Jupiter-sized gas giants can have as many as seven habitable planets!

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The Giant Planets in the Solar System Stunted the Growth of Mars

A new study led by researchers from OU indicates that the outer planets could be why Mars is significantly smaller than Earth. Credit: NASA

For centuries, astronomers and scientists have sought to understand how our Solar System came to be. Since that time, two theories have become commonly-accepted that explain how it formed and evolved over time. These are the Nebular Hypothesis and the Nice Model, respectively. Whereas the former contends that the Sun and planets formed from a large cloud of dust and gas, the latter maintains the giant planets have migrated since their formation.

This is what has led to the Solar System as we know it today. However, an enduring mystery about these theories is how Mars came to be the way it is. Why, for example, is it significantly smaller than Earth and inhospitable to life as we know it when all indications show that it should be comparable in size? According to a new study by an international team of scientists, the migration of the giant planets could have been what made the difference.

For over a decade, astronomers have been operating under the assumption that shortly after the formation of the Solar System, the gas and ice giants of the outer Solar System (Jupiter, Saturn, Uranus and Neptune) began to migrate outward. This is the substance of the Nice Model, which asserts that this migration had a profound effect on the evolution of the Solar System and the formation of the terrestrial planets.

This model – named for the location of the Observatoire de la Côte d’Azur (in Nice, France), where it was initially developed – began as an evolutionary model that helped explain the observed distributions of small objects like comets and asteroids. As Matt Clement, a graduate student in the HL Dodge Department of Physics and Astronomy at the University of Oklahoma and the lead author on the paper, explained to Universe Today via email:

“In the model, the giant planets (Jupiter, Saturn, Uranus and Neptune) originally formed much closer to the Sun.  In order to reach their current orbital locations, the entire solar system undergoes a period of orbital instability.  During this unstable period, the size and the shape of the giant planet’s orbits change rapidly.”

For the sake of their study, which was recently published in the scientific journal Icarus under the title “Mars Growth Stunted by an Early Giant Planet Instability“, the team expanded on the Nice Model. Through a series of dynamical simulations, they attempted to show how, during the early Solar System, the growth of Mars was halted thanks to the orbital instabilities of the giant planets.

The purpose of their study was also to address a flaw in the Nice Model, which is how the terrestrial planets could have survived a serious shake up of the Solar System. In the original version of the Nice Model, the instability of the giant planets occurred a few hundred million years after the planets formed, which coincided with the Late Heavy Bombardment – when the inner Solar System was bombarded by a disproportionately large number of asteroids.

This period is evidenced by spike in the Moon’s cratering record, which was inferred from an abundance of samples from the Apollo missions with similar geological dates. As Clement explained:

“A problem with this is that it is difficult for the terrestrial planets (Mercury, Venus, Earth and Mars) to survive the violent instability without being ejected out of the solar system or colliding with one another. Now that we have better, high resolution images of lunar craters and more accurate methods for dating the Apollo samples, the evidence for a spike in lunar cratering rates is diminishing. Our study investigated whether moving the instability earlier, while the inner terrestrial planets were still forming, could help them survive the instability, and also explain why Mars is so small relative to the Earth.”

Clement was joined by Nathan A. Kaib, a OU astrophysics professor, as well as Sean N. Raymond of the University of Bordeaux and Kevin J. Walsh from the Southwest Research Institute. Together, they used the computing resources of the OU Supercomputing Center for Education and Research (OSCER) and the Blue Waters supercomputing project to perform 800 dynamical simulations of the Nice model to determine how it would impact Mars.

These simulations incorporated recent geological evidence from Mars and Earth that indicate that Mars’ formation period was about 1/10th that of Earth’s. This has led to the theory that Mars was left behind as a “stranded planetary embryo” during the formation of the Sun’s inner planets. As Prof. Kaib explained to Universe Today via email, this study was therefore intended to test how Mars emerged from planetary formation as a planetary embryo:

“We simulated the “giant impact phase” of terrestrial planet formation (the final stage of the formation process). At the beginning of this phase, the inner Solar System (0.5-4 AU) consists of a disk of about 100 moon-to-mars-sized planetary embryos embedded in a sea of much smaller, more numerous rocky planetesimals. Over the course of 100-200 million years the bodies making up this system collide and merge into a handful (typically 2-5) rocky planetary mass bodies. Normally, these types of simple initial conditions build planets on Mars-like orbits that are about 10x more massive than Mars. However, when the terrestrial planet formation process is interrupted by the Nice model instability, many of the planet building blocks near the Mars region are lost or tossed into the Sun. This limits the growth of Mars-like planets and produces a closer match to our actual inner solar system.”

Size comparison between Earth and Mars. Credit: NASA

What they found was that this revised timeline explained the disparity between Mars and Earth. In short, Mars and Earth vary considerably in size, mass and density because the giant planets became unstable very early in the Solar System’s history. In the end, this is what allowed Earth to become the only life-bearing terrestrial planet in the Solar System, and for Mars to become the cold, desiccated and thinly-atmosphered place that it is today.

As Prof. Kaib explained, this is not the only model for explaining the disparity between Earth and Mars, but the evidence all fits:

“Without this instability, Mars likely would have had a mass closer to Earth’s and would be a very different, perhaps more Earth-like, planet compared to what it is today,” he said. “I should also say that this is not the only mechanism capable of explaining the low mass of Mars. However, we already know that the Nice model does an excellent job of reproducing many features of the outer Solar System, and if it occurs at the right time in the Solar System’s history it also ends up explaining our inner Solar System.”

This study could also have drastic implications when it comes to the study of extra-solar systems. At present, our models for how planets form and evolve are based on what we have been able to learn from our own Solar System. Hence, by learning more about how gas giants and terrestrial planets grew and assumed their current orbits, scientists will be able to create more comprehensive models of how life-bearing planets could merge around other stars.

It certainly would help narrow the search for “Earth-like” planets and (dare we dream?) planets that support life.

Further Reading: University of Oklahoma, Icarus

How Many of Earth’s Moons Crashed Back Into the Planet?

Artist's concept of a collision between proto-Earth and Theia, believed to happened 4.5 billion years ago. Credit: NASA

For decades, scientists have pondered how Earth acquired its only satellite, the Moon. Whereas some have argued that it formed from material lost by Earth due to centrifugal force, or was captured by Earth’s gravity, the most widely accepted theory is that the Moon formed roughly 4.5 billion years ago when a Mars-sized object (named Theia) collided with a proto-Earth (aka. the Giant Impact Hypothesis).

However, since the proto-Earth experienced many giant-impacts, several moons are expected to have formed in orbit around it over time. The question thus arises, what happened to these moons? Raising this very question, a team an international team of scientist conducted a study in which they suggest that these “moonlets” could have eventually crashed back into Earth, leaving only the one we see today.

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How Long Can a Rocky World Withstand the Blasts From a Red Dwarf Star?

Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser

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.

Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. Credits: NASA/GSFC

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.”

At one time, Mars had a magnetic field similar to Earth, which prevented its atmosphere from being stripped away. Credit: NASA

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.

To receive the same amount of starlight as Mars receives from our Sun, a planet orbiting an M-type red dwarf would have to be positioned much closer to its star than Mercury is to the Sun. Credit: NASA’s Goddard Space Flight Center

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.”

Multiple survey have revealed evidence of rocky planets orbiting a red dwarf stars, raising questions about their habitability. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).

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.

Other panelists that took part in the presentations included Giada Arney and Katherine Garcia-Sage of NASA Goddard Space Flight Center and Stephen Kane of the University of California-Riverside. You can access the press conference materials by going to NASA Goddard Media Studios.

Further Reading: NASA, AGU

Looking for Signs of Life on Distant Planets Just Got Easier

This illustration shows a star's light illuminating the atmosphere of a planet. Credits: NASA Goddard Space Flight Center

When it comes to searching for worlds that could support extra-terrestrial life, scientists currently rely on the “low-hanging fruit” approach. Since we only know of one set of conditions under which life can thrive – i.e. what we have here on Earth – it makes sense to look for worlds that have these same conditions. These include being located within a star’s habitable zone, having a stable atmosphere, and being able to maintain liquid water on the surface.

Until now, scientists have relied on methods that make it very difficult to detect water vapor in the atmosphere’s of terrestrial planets. But thanks to a new study led by Yuka Fujii of NASA’s Goddard Institute for Space Studies (GISS), that may be about to change. Using a new three-dimensional model that takes into account global circulation patterns, this study also indicates that habitable exoplanets may be more common than we thought.

The study, titled “NIR-driven Moist Upper Atmospheres of Synchronously Rotating Temperate Terrestrial Exoplanets“, recently appeared in The Astrophysical Journal. In addition to Dr. Fujii, who is also a member of the Earth-Life Science Institute at the Tokyo Institute of Technology, the research team included Anthony D. Del Genio (GISS) and David S. Amundsen (GISS and Columbia University).

Artist’s concept of the hot Jupiter WASP-121b, which presents the best evidence yet of a stratosphere on an exoplanet – generated using Engine House VFX. Credit: Bristol Science Centre/University of Exeter

To put it simply, liquid water is essential to life as we know it. If a planet does not have a warm enough atmosphere to maintain liquid water on its surface for a sufficient amount of time (on the order of billions of years), then it is unlikely that life will be able to emerge and evolve. If a planet is too distant from its star, its surface water will freeze; if it is too close, its surface water will evaporate and be lost to space.

While water has been detected in the atmospheres of exoplanets before, in all cases, the planets were massive gas giants that orbited very closely to their stars. (aka. “Hot Jupiters”). As Fujii and her colleagues state in their study:

“Although H2O signatures have been detected in the atmospheres of hot Jupiters, detecting molecular signatures, including H2O, on temperate terrestrial planets is exceedingly challenging, because of the small planetary radius and the small scale height (due to the lower temperature and presumably larger mean molecular weight).”

When it comes to terrestrial (i.e. rocky) exoplanets, previous studies were forced to rely on one-dimensional models to calculate the presence of water. This consisted of measuring hydrogen loss, where water vapor in the stratosphere is broken down into hydrogen and oxygen from exposure to ultraviolet radiation. By measuring the rate at which hydrogen is lost to space, scientists would estimate the amount of liquid water still present on the surface.

Artist’s impression of the “Venus-like” exoplanet GJ 1132b. Credit: cfa.harvard.edu

However, as Dr. Fujii and her colleagues explain, such models rely on several assumptions that cannot be addressed, which include the global transport of heat and water vapor vapor, as well as the effects of clouds. Basically, previous models predicted that for water vapor to reach the stratosphere, long-term surface temperatures on these exoplanets would have to be more than 66 °C (150 °F) higher than what we experience here on Earth.

These temperatures could create powerful convective storms on the surface. However, these storms could not be the reason water reaches the stratosphere when it comes to slowly rotating planets entering a moist greenhouse state – where water vapor intensifies heat. Planets that orbit closely to their parent stars are known to either have a slow rotation or to be tidally-locked with their planets, thus making convective storms unlikely.

This occurs quite often for terrestrial planets that are located around low-mass, ultra cool, M-type (red dwarf) stars. For these planets, their proximity to their host star means that it’s gravitational influence will be strong enough to slow down or completely arrest their rotation. When this occurs, thick clouds form on the dayside of the planet, protecting it from much of the star’s light.

The team found that, while this could keep the dayside cool and prevent water vapor from rising, the amount of near-Infrared radiation (NIR) could provide enough heat to cause a planet to enter a moist greenhouse state. This is especially true of M-type and other cool dwarf stars, which are known to produce more in the way of NIR. As this radiation warms the clouds, water vapor will rise into the stratosphere.

Artist’s impression of Proxima b, the closest exoplanet to the Solar System. In the background, the binary system of Alpha Centauri can be seen. Credit: ESO/M. Kornmesser

To address this, Fujii and her team relied on three-dimensional general circulation models (GCMs) which incorporate atmospheric circulation and climate heterogeneity. For the sake of their model, the team started with a planet that had an Earth-like atmosphere and was entirely covered by oceans. This allowed the team to clearly see how variations in distance from different types of stars would effect conditions on the planets surfaces.

These assumptions allowed the team to clearly see how changing the orbital distance and type of stellar radiation affected the amount of water vapor in the stratosphere. As Dr. Fujii explained in a NASA press release:

“Using a model that more realistically simulates atmospheric conditions, we discovered a new process that controls the habitability of exoplanets and will guide us in identifying candidates for further study… We found an important role for the type of radiation a star emits and the effect it has on the atmospheric circulation of an exoplanet in making the moist greenhouse state.”

In the end, the team’s new model demonstrated that since low-mass star emit the bulk of their light at NIR wavelengths, a moist greenhouse state will result for planets orbiting closely to them. This would result in conditions on their surfaces that comparable to what Earth experiences in the tropics, where conditions are hot and moist, instead of hot and dry.

Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO

What’s more, their model indicated that NIR-driven processes increased moisture in the stratosphere gradually, to the point that exoplanets orbiting closer to their stars could remain habitable. This new approach to assessing potential habitability will allow astronomers to simulate circulation of planetary atmospheres and the special features of that circulation, which is something one-dimensional models cannot do.

In the future, the team plans to assess how variations in planetary characteristics -such as gravity, size, atmospheric composition, and surface pressure – could affect water vapor circulation and habitability. This will, along with their 3-dimensional model that takes planetary circulation patterns into account, allow astronomers to determine the potential habitability of distant planets with greater accuracy. As Anthony Del Genio indicated:

“As long as we know the temperature of the star, we can estimate whether planets close to their stars have the potential to be in the moist greenhouse state. Current technology will be pushed to the limit to detect small amounts of water vapor in an exoplanet’s atmosphere. If there is enough water to be detected, it probably means that planet is in the moist greenhouse state.”

Beyond offering astronomers a more comprehensive method for determining exoplanet habitability, this study is also good news for exoplanet-hunters hoping to find habitable planets around M-type stars. Low-mass, ultra-cool, M-type stars are the most common star in the Universe, accounting for roughly 75% of all stars in the Milky Way. Knowing that they could support habitable exoplanets greatly increases the odds of find one.

Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech
Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech

In addition, this study is VERY good news given the recent spate of research that has cast serious doubt on the ability of M-type stars to host habitable planets. This research was conducted in response to the many terrestrial planets that have been discovered around nearby red dwarfs in recent years. What they revealed was that, in general, red dwarf stars experience too much flare and could strip their respective planets of their atmospheres.

These include the 7-planet TRAPPIST-1 system (three of which are located in the star’s habitable zone) and the closest exoplanet to the Solar System, Proxima b. The sheer number of Earth-like planets discovered around M-type stars, coupled with this class of star’s natural longevity, has led many in the astrophysical community to venture that red dwarf stars might be the most likely place to find habitable exoplanets.

With this latest study, which indicates that these planets could be habitable after all, it would seem that the ball is effectively back in their court!

Further Reading: NASA, The Astrophysical Journal