Kepler brings TRAPPIST-1's outermost planet into focus
As exciting as it was, the recent discovery of the TRAPPIST-1 system and its seven potentially habitable planets still left scientists with plenty of questions. One area where they were really left in the dark regarded the system's outermost planet, TRAPPIST-1h. A new study using data from prolific exoplanet hunting telescope Kepler has now filled in some of the blanks on this cold and lonely body, bringing to light new information on its orbit, temperature and chances of hosting life.
Scientists are unable to directly image exoplanets, due to the blinding light from the parent star. Instead, the planets are detected when they pass in front of this star and create a dip in the light. The Kepler Space Telescope has identified thousands of exoplanets in this way, and it has now offered a new look at one of the more promising exoplanet systems to date.
Before this latest study, scientists looking at the planet TRAPPIST-1h had only observed it in a single one of these transits, leaving them little to work with. But now, led by University of Washington doctoral student Rodrigo Luger, researchers have drawn on 79 days of observational data from Kepler to catch four of these transits in action.
This still presented challenges. One transit, for example, coincided with the transit of TRAPPIST-1b, the closest planet to the system's host star. Another coincided with a stellar flare. But still, the data enabled the team to confirm that TRAPPIST-1h orbits the parent star, which lies 40 light years away from Earth, every 18.77 days with an average temperature of 173 Kelvin (-148° F, or -100° C).
The planet's orbit actually lines up perfectly with the scientists' estimates prior to the new Kepler data. By studying the orbital velocities of the system's other six planets, they had some idea of the orbital velocity of TRAPPIST-1h, thanks to interplanetary relationships called orbital resonance.
These relationships are seen elsewhere in the universe, and involve planets whose orbital periods are mathematically related, with each orbit forming a number ratio to its neighbors. With regard to TRAPPIST-1, a study earlier this month revealed that it is actually how all seven planets are able to orbit in such close proximity to their star – all tighter than that of Mercury to our Sun – without crashing into one another. The new study further consolidates this seven-planet orbital resonance theory, and the scientists believe that the interplay was formed early in the life of the TRAPPIST-1 system, before the planets and orbits were fully formed.
"We could therefore be looking at a planet that was once habitable and has since frozen over, which is amazing to contemplate and great for follow-up studies," Luger said.
The research was published in the journal Nature Astronomy.
Source: University of Washington