Rocky, salmon-y and possibly with an ocean or two

SEVEN PLANETS, each of diameter within 25% more or less of Earth’s, orbiting a star 40 light years — or 235 trillion miles — away, have thrown up the first realistic opportunity to search for signs of alien life outside the Solar System. The star at the centre of the System is called TRAPPIST-1, after the Transiting Planets and Planetesimals Small Telescope, a robotic telescope in Chile’s Atacama Desert that astronomers initially used to study it.

“This is the first time so many planets of this kind are found around the same star,” Michael Gillon, an astronomer at the University of Liege in Belgium and the leader of an international team that has been observing TRAPPIST-1, said at a telephone news conference organised by the journal Nature, which published the findings on Wednesday.

In making the discovery, Amaury HMJ Triaud, an astronomer at Cambridge in England and another member of the research team, said, “we have taken a crucial step toward finding if there is life out there”. “Here, if life managed to thrive and releases gases similar to that we have on Earth, then we will know.”

Even if the planets all turn out to be lifeless, scientists will have learned more about what keeps life from flourishing. The authors of the Nature paper include Didier Queloz, one of the astronomers who discovered in 1995 the first known exoplanet — a planet outside the Solar System — around a Sun-like star.

Astronomers watching TRAPPIST-1 found it periodically dimmed, indicating that a planet might be passing in front of it, blocking partofthestarlight.fromtheshapeofthedips, they calculated the size of the planet, and TRAPPIST-1’S light dipped so many times that they reported there was more than 1 planet.

All 7 planets are very close to the star, circling more quickly than the planets in our Solar System. The innermost completes an orbit — a ‘year’ in Earth terms — in just 1.5 days; the farthest in about 20 days.

Because TRAPPIST-1 is a “cool” star, the planets’ surfaces could be at the right temperatures to have water flow, one of the essential ingredients for life. The fourth, fifth and sixth planets — called TRAPPIST-1E, f and g — orbit in the star’s “habitable zone”, and could have oceans. While this isn’t confirmed yet, what is indeed confirmed is that the 2 innermost planets — TRAPPIST-1B and TRAPPIST-1C — are not enveloped in hydrogen. Which means they are rocky like Earth. If observations over the coming months or years reveal oxygen in the atmosphere of any of the planets, especially along with methane, ozone and carbon dioxide in certain proportions, the existence of life could be expected with “99% confidence”, the scientists said.

The scientists expected the star to be a deep red, but with most of its light emitted at infrared wavelengths and out of view of human eyes, we would perhaps “see something more salmon-y”, they said. — THE NYT 1.51 0.011 1.09R 0.85M 2.42 0.015 1.06R 1.38M 4.05 0.021 0.77R 0.41M 6.10 0.028 0.92R 0.62M 9.21 0.037 1.04R 0.68M 12.35 0.045 1.13R 1.34M ORBITAL PERIOD DISTANCE TO STAR PLANET RADIUS PLANET MASS ORBITAL PERIOD (DAYS) ~20 ~0.06 0.76R —

Even if the planets all turn out to be lifeless, scientists will have learned more about what keeps life from flourishing.

Days Astronomical Units (AU) relative to earth relative to earth