Scientists pleased with TESS exoplanet mission

by

SEATTLE — As the first discoveries from a new NASA exoplanet mission start rolling in, project officials are planning for the first in what they hope to be a series of extended missions for the spacecraft.

During a briefing at the 233rd meeting of the American Astronomical Society here Jan. 7, scientists working on the Transiting Exoplanet Survey Satellite (TESS) mission announced that they have already discovered three planets, each smaller than Neptune, orbiting stars within 100 light-years of the solar system.

The most recent of the three planets, HD 21749b, orbits a star 53-light years away with an estimated mass 23 times that of Earth. The star it orbits may have a second planet, about the size of the Earth, orbiting closer in, said Chelsea Huang of the Massachusetts Institute of Technology (MIT) at the briefing.

The discoveries come from data from the first few months of TESS operations, covering four of a planned 26 sectors of the sky that the spacecraft will observe over the next two years. The spacecraft, launched in April 2018 on a SpaceX Falcon 9, started science observations in July. “We’ve made great progress using three months of data,” said Huang.

Scientists involved with TESS said the early results show the potential of the spacecraft to help discover many more small exoplanets around nearby, bright stars, excellent candidates for follow-up observations by other observatories, including the James Webb Space Telescope.

“The very best targets that Webb will be able to spend time studying in detail spectroscopically are, of necessity, going to be the bright targets that TESS will actually find,” said George Ricker, principal investigator for TESS at MIT, at the briefing.

Ricker and others involved with the mission hope that the exoplanet discoveries and other astrophysical phenomena, such as supernova explosions, detected in images from the spacecraft will continue for many years to come.

For now, TESS is about one-fourth the way through a two-year primary mission. However, planning is already underway for one extended mission, Ricker said. That extended mission, lasting a little more than two years from mid-2020 to late 2022, would revisit some areas of the sky observed in the prime mission as well as fill in some gaps not observed.

The proposal for that extended mission, which will be part of the overall senior review of astrophysics missions, is due to NASA Feb. 1. Ricker said that the ongoing partial government shutdown, which affects NASA, could push back that schedule.

Ricker is hopeful that the extended mission is the first of many for TESS. The spacecraft is in excellent condition, with camera performance and stability far better than anticipated. The spacecraft’s reaction wheels — which caused problems for another exoplanet mission, Kepler — are based on designs with commercial satellite heritage that should last for decades, and the spacecraft’s reserves of hydrazine fuel, used at a rate of one gram a week for momentum management, can last for far longer.

At the briefing, Ricker showed a chart of extended missions going out through the 2020s. Those additional extended missions, he said, could support a wide range of other spacecraft and groundbased observatories that can study exoplanets in further detail, such as the Wide-Field Infrared Survey Telescope (WFIRST) and ESA’s Planetary Transits and Oscillations or stars, or PLATO, spacecraft.

“In my plot I only put out extended missions running 10 years,” Ricker said, “but if NASA is patient with the mission and funds us properly, I think we could probably go for several decades.”