One of the main goals of the James Webb Space Telescope (JWST) is to detect atmospheres around exoplanets to find out whether or not they could potentially harbor life. To do this, however, scientists need to know where to look, and the exoplanet must actually have an atmosphere. While scientists currently know the location of about 6,000 exoplanets, they also believe that many of them do not have atmospheres and that many of those that do do are not actually the size of Earth. And many of them are near stars that are too bright for our current telescopes to see their atmospheres. All of these limitations ultimately mean that even with 6,000 potential candidates, the number of Earth-sized specimens for which we could find an atmosphere is relatively small. So a new paper available on arXiv from Cal Tech’s Jonathan Barrientos and his co-authors that describes five new exoplanets around M dwarf stars – two of which could potentially have an atmosphere – is big news for astrobiologists and exoplanet hunters alike.
The Transiting Exoplanet Survey Satellite (TESS) has discovered these five candidates, but additional work is required to “confirm” them, which is reported for the first time in this new paper. When TESS finds a potentially interesting signal, its operators issue a TESS Object of Interest (TOI) alert, informing the public about a new exoplanet candidate. Confirming a candidate typically requires follow-up observations such as transit photometry or perhaps even high-resolution imaging.
Doing this for these planets was truly a team effort, involving data from at least nine different telescopes, including the Keck II Observatory and the Hale Telescope. All of this data served to confirm the existence of five planets in four separate systems – one system had two planets resonating with each other. Four of these were “super-Earths” between 1.28 and 1.56 times the size of our planet, while the other, known as TOI-5716b, was roughly the size of Earth.
Fraser discusses exoplanet atmospheres with Dr. Joanna Barstow
A key difference between our home planet and those found around distant stars is their orbital period. They ranged from 0.6 to 11.5 days, which is obviously absurdly fast, but is fairly normal for most current exoplanet candidates given the limited telescope time available to them. But perhaps more importantly, they are all close to M dwarf stars.
This is important for two reasons. First, M dwarfs are relatively dim, meaning it is much easier for a telescope like the James Webb Space Telescope to block out the star’s light while trying to resolve an atmosphere. But on the other hand, they are also notoriously volatile, with massive X-ray and ultraviolet flares that can “sandblast” a planet’s atmosphere if they are too close to the star.
Scientists explain this sandblasting effect by estimating a “cosmic coastline.” It represents a diagram between the “insolation” (i.e. sunlight/radiation) a planet receives and its gravity. At higher levels of solar radiation, planets’ atmospheres are more easily blown away. But higher masses allow a planet to maintain a tighter grip on its atmosphere. This depiction of solar radiation and gravity draws a very clear, linear line that scientists call the cosmic coastline.
Fraser discusses the technology we need to truly observe Earth-like exoplanets.
In the work, the five planets are actually divided into three categories. Three of the planets are clearly “above” the cosmic coastline, meaning the energy from their stars has likely blasted away any atmosphere they may have had. A fourth planet, TOI-5736b, the one with the shortest period, is in a category of its own, because although it receives a ton of radiation, its large radius and mass mean it could at least theoretically maintain a volatile (i.e. heavy) atmosphere simply because it is so large.
This leaves one outstanding: the exoplanet TOI-5728b. Although it orbits an active M dwarf star, this exoplanet’s atmosphere appears to be sufficient to maintain its atmosphere. Combined with the fact that M dwarfs are very faint, this planet is an excellent candidate for follow-up observation by the James Webb Space Telescope (JWST) to attempt direct atmospheric detection.
Realistically, however, with an orbital period of 11.5 days, the likelihood of complex life on this newly confirmed planet is slim. But some extremophiles could potentially secure a livelihood if they were adequately protected. We won’t know until we look, and this journey from TOI discovery through confirmation and characterization to eventual observation by some of the world’s most sought-after observatories is exactly how science is supposed to work.
It might be a while before JWST, which is obviously very busy, can focus its attention on this one particular planet. At some point, however, we should get some data about its atmosphere that will delight both planetary scientists and astrobiologists. You just have to wait a little longer as the wheels of science continue to turn.
Learn more:
JG Barrientos et al. – From Earth to Super-Earth: Five new small planets transiting M dwarf stars
UT – Warm exo-titans as a test of planetary atmospheric diversity
UT – GJ 12 b: Earth-sized planet orbiting a quiet M dwarf star
UT – Scientists find the strongest evidence yet for an atmosphere on a molten rocky exoplanet
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