“Lost Worlds” of the TESS Mission

"Lost Worlds" of the TESS Mission


A “lost world,” exoplanet NGTS-11b, the size and mass of Saturn with an orbit of thirty-five days around a star 620 light years away, is located five times closer to its sun than Earth is to our own. The planet is among hundreds of alien worlds that astronomers, using NASA’s alien-planet-hunting TESS telescope data, are pioneering a new method to track down and characterize in the hope of finding cooler, potentially habitable planets.

The planet was originally found in a search for planets in 2018 by a University of Warwick-led team based on TESS using the transit method to spot planets, scanning for the telltale dip in light from the star that indicates that an object has passed between the telescope and the star.

In 2018, astronomers not involved with the University of Warwick study identified the Galactic Habitable Zone (GHZ), a particularly favorable location in the Milky Way for life, with our Solar System sitting near its center. It has taken almost all of 5 billion years for intelligence to evolve on Earth, and if that is typical, we may be one of the first intelligent civilizations in our Galaxy. There is indeed something that appears to be unique about our place the Milky Way, in both time and space.

Within the habitable zone, observes George Johnson in the New York Times: “rerun the tape of evolution, and DNA, RNA, ATP, the Krebs cycle — the rigmarole of Biology 101 — would probably arise again, here or in distant worlds.”

TESS only scans most sections of the sky for 27 days, which means many of the longer period planets only transit once in the spacecrafts data. And without a second observation the planet is effectively lost. The University of Warwick led team followed up one of these ‘lost’ planets using the telescopes at the Next-Generation Transit Survey (NGTS) in Chile and observed the star for seventy-nine nights, eventually catching the planet transiting for a second time nearly a year after the first detected transit.

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“By chasing that second transit down we’ve found a longer period planet. It’s the first of hopefully many such finds pushing to longer periods,” said physicist Samuel Gill at the University of Warwick.”These discoveries are rare but important, since they allow us to find longer period planets than other astronomers are finding. Longer period planets are cooler, more like the planets in our own solar system. NGTS-11b has a temperature of only 160°C—cooler than Mercury and Venus. Although this is still too hot to support life as we know it, it is closer to the Goldilocks zone than many previously discovered planets which typically have temperatures above 1000°C.”

“This planet is out at a thirty-five days orbit, which is a much longer period than we usually find them. It is exciting to see the Goldilocks zone within our sights,” said co-author Dr. Daniel Bayliss also at the University of Warwick.

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“There are hundreds of single transits detected by TESS that we will be monitoring using this method,” Gill adds. “This will allow us to discover cooler exoplanets of all sizes, including planets more like those in our own solar system. Some of these will be small rocky planets in the Goldilocks zone that are cool enough to host liquid water oceans and potentially extraterrestrial life.”

Source: Samuel Gill et al. NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event, The Astrophysical Journal (2020). DOI: 10.3847/2041-8213/ab9eb9

The Daily Galaxy, Sam Cabot, via University of Warwick

Image credit top of page: With thanks to Ricardo Ramirez