An artist’s impression of the seven TRAPPIST planets, with -1b lower left and -1h lower right. The three planets in the star’s habitable zone, -!e, -1f and -1g are the right-hand three in the top row. Credit: NASA
I recently wrote a space update special on the TRAPPIST-1 star system with its seven roughly Earth-sized planets. Since then, there has been speculation about whether any of them might support life, and what conditions for life might be like.
Whether life may have arisen on any of the worlds is tough question to answer. Three of the seven lie within the “habitable zone” where liquid water might exist (TRAPPIST-1e, -1f and -1g) – which is a positive for life as we know it. But for that liquid water to remain liquid, the planets must have an atmosphere. Currently, only TRAPPIST-1b and -1c have, through spectral analysis, been shown to harbour atmospheres, but these seem to be limited in scope, and could range from a water vapour rich atmosphere through to an environment similar to that of Venus.
On the negative side of the equation, the nature of their parent star, a super cool red dwarf with all internal action entirely convective in nature, means that all seven planets are likely subject to sufficient irradiation in the X-ray and extreme ultraviolet wavelengths to significantly alter their atmospheres, potentially rendering them unsuitable for life. Further, all seven are tidally locked, meaning they always keep the same face towards their parent star. This will inevitably give rise to extreme conditions, with one side of each world bathed in perpetual daylight and the other in perpetual, freezing darkness, resulting in extreme atmospheric movements and likely harsh weather.
Comparing the TRAPPIST-1 system with the solar system. Credit: European Southern Observatory / O. Furtak
Daylight on the planets would also be very different. Although one side of these worlds be forever in daytime, and despite the relative proximity with which they orbit their parent star, days on their surfaces would never be much brighter than sunset here on Earth, both in terms of colour and light intensity. This is because most of the light emitted by TRAPPIST-1 is radiated in the infra-red wavelengths, rather than visible wavelengths.
One the more positive side of the equation, despite the low levels of visible light, TRAPPIST-1 could still be able to sufficiently warm an atmospheres the planets might have, and the weather conditions might actually dissipate this warmth evenly over the planet’s surface, perhaps making it more hospitable to life.
It’s also likely the planets experience a lot of tidal flexing as they come under the influence of one another as well as their parent star. This flexing might give rise to hydrothermal and volcanic vents, which in turn could provide the necessary heat (energy), minerals and chemicals necessary to kick-start basic life.
Artist’s impression of the three planets in TRAPPIST-1’s habitable zone and to scale relative to one another. -1e (l) is the most likely to have extensive liquid water. It is 92% as big as Earth, with a mass of 62% that of Earth. It orbits its parent star about 10.8 times the distance from Earth to the Moon. -1f (c) is 1.04 times the size of Earth, but also with 62% of its mass. It is potentially water rich, and gets as much light from its star as Mars does from the Sun. -1g (r) is the outermost of the three. It is 1.13 times Earth’s size with 1.34 times its mass. It is far enough away from its parent star that the surface is likely to be entirely frozen, but the gravitational influence of the other planets could give rise to a liquid water ocean under the ice. Credit: NASA
Studies of the TRAPPIST system will continue using the Spitzer and Hubble space telescopes and via ground-based observatories. However, as mentioned in my special report, it is likely to be the James Webb Space Telescope which will hopefully reveal many of the secrets of the TRAPPIST-1 system.
That said, and for those still wondering about intelligent life arising on any of these worlds, SETI, the Search for Extra-Terrestrial Intelligence has been “listening in” on the star for indications of radio traffic for some time (pre-dating the discovery of the first two planets in the system in 2016). Those surveys haven’t revealed any kind of radio emissions from the system that might be of artificial origin, but now we know there are seven planets, SETI has marked TRAPPIST-1 for further investigations with their Allen Telescope Array (ATA).
A Further Clue in the Hunt for Planet 9
Last year, Caltech astronomers Mike Brown and Konstantin Batygin found indirect evidence for the existence of a large planet in the outer reaches of our Solar System well beyond Pluto; since then, the search has been on. I first covered the hunt in January 2016, and followed it with updates in February 2016 and October 2016, and it now seems a new clue to the planet’s existence may have been revealed.
Planet X, if it exists,could equal Neptune in size, and orbits the Sun 200 times further away than Earth. Credit: Caltech / R. Hurt
Astronomers using the Gran Telescopio CANARIAS (GTC) in the Canary Islands looked at two distant asteroids, called Extreme Trans Neptunian Objects (ETNOs). Spectroscopic observations 2004 VN112 and 2013 RF98 suggest that the two were once a binary asteroid pairing that were pulled apart as a result of the influence of a mass massive body between 10 and 20 Earth masses in size and about 300 to 600 AU from the Sun. As a result of this, the two bodies drew further and further apart over, time they became more and more separated to become how we see them today.
“The similar spectral gradients observed for the pair 2004 VN112 – 2013 RF98 suggests a common physical origin,” said Julia de León, an astrophysicist at the Instituto de Astrofísica de Canarias (IAC). “We are proposing the possibility that they were previously a binary asteroid which became unbound during an encounter with a more massive object.”
de León and his team carried out thousands of computer-based simulations to see how this might have happened, and found the most consistent result suggested the bodies were separated as a result of a close passage by a massive planetary object around 5-10 million years ago.
As it might be: estimates concerning Planet Nine’s possible size, mass, etc., should it exist. Credit: Space.com / Karl Tate
What is particularly interesting here is that the location of the two asteroids, coupled with the suggested mass of the body which pulled them apart and the distance it is believed to have been from the Sun, also fit the broader parameters for where the orbit of Planet 9 might reside, and the estimated mass of the planet. Thus, when combined with the eccentric orbits of several Kuiper Belt Objects believed to have been perturbed in their orbits around the Sun by planet 9, it gives further credence to the idea it really is out there, somewhere.
When – and if – it might eventually be found is open to question. However, it is hoped that a recently started “citizen scientist project will encourage amateur astronomers around the world to join in the hunt for Planet 9.