TRAPPIST-1's outermost planet orbits every 19 days: NASA

By PTI Published on May 23, 2017 01:45 PM IST

Washington: A year in the outermost planet of the recently discovered TRAPPIST-1 star system would last just 19 Earth days, say scientists who have confirmed the orbital details of the cosmic body using NASA's Kepler Telescope.

Researchers identified a regular pattern in the revolutions of the planets of TRAPPIST-1 and confirmed details about the orbit of its least understood planet, TRAPPIST-1h.

TRAPPIST-1 is only eight per cent the mass of our Sun, making it a cooler and less luminous star. It is home to seven Earth-size planets, three of which orbit in their star's habitable zone - the range of distances from a star where liquid water could pool on the surface of a rocky planet.

The system is located about 40 light-years away in the constellation of Aquarius and is estimated to be between three billion and eight billion years old. Scientists announced that the system has seven Earth- sized planets at a NASA press conference on February 22.

NASA's Spitzer Space Telescope, the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) in Chile and other ground-based telescopes were used to detect and characterise the planets. However, researchers only had a rough estimate for the orbital period of TRAPPIST-1h.

Astronomers from the University of Washington in the US have used data from the Kepler spacecraft to confirm that TRAPPIST-1h orbits its star every 19 days. At six million miles from its cool dwarf star, TRAPPIST- 1h is located beyond the outer edge of the habitable zone, and is likely too cold for life as we know it.

The amount of energy planet h receives from its star is comparable to what the dwarf planet Ceres, located in the asteroid belt between Mars and Jupiter, gets from our Sun.

"It's incredibly exciting that we're learning more about this planetary system elsewhere, especially about planet h, which we barely had information on until now," said Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate.

"This finding is a great example of how the scientific community is unleashing the power of complementary data from our different missions to make such fascinating discoveries," said Zurbuchen. Using the prior Spitzer data, researchers recognised a mathematical pattern in the frequency at which each of the six innermost planets orbits their star.

This complex but predictable pattern, called an orbital resonance, occurs when planets exert a regular, periodic gravitational tug on each other as they orbit their star.

The Kepler spacecraft stared at the patch of sky home to the TRAPPIST-1 system from December 15 last year to March 4 collecting data on the star's minuscule changes in brightness due to transiting planets. On March 8, the raw, uncalibrated data was released to the scientific community to begin follow-up studies.

The work to confirm TRAPPIST-1h's orbital period immediately began and scientists from around the world took to social media to share in real-time the new information gleaned about the star's behaviour and its brood of planets.

Within two hours of the data release, the team confirmed their prediction of a 19-day orbital period.