Editor's note: A version of this was previously published on the author'swebsite.
TESS, which is NASA's Transiting Exoplanet Survey Satellite, has completed its first run of a two-year project, surveying nearby stars south of the equator and making impressive discoveries. It now turns its four cameras to the north.
This latest of NASA's exoplanet hunters is designed to check relatively nearby stars for evidence of other worlds — planets that may be close enough to eventually examine their atmospheres and look for indications of life.
In transiting searches, sensitive cameras detect exoplanets by noticing the slight dimming of starlight when planets move across the faces of their stars. To be verified, a target must repeat transits at least three times as observed by the space cameras; then follow-up observations by Earth-based telescopes are required to show whether the dimming was caused by starspots (equivalent to sunspots), a "companion" star, glitches in the equipment or actual planetary eclipses.
TESS is the successor to the Kepler exoplanet surveyor, which was launched in March 2009 and mostly examined a region of space 12 degrees by 12 degrees, "the size of the palm of your hand at arm's length," said Jason H. Steffen, associate professor in the Department of Physics and Astronomy, University of Nevada, Las Vegas, who joined NASA's planet-hunting team in 2008.
Before its fuel ran out in October 2018, Kepler had detected 2,730 planets that have been confirmed by now, plus 2,774 that are yet to be proven, in a pair of different project configurations.
Kepler's field of view was restricted, preventing it from scoping out stars in most regions of the sky. But TESS is charged with surveying stars within 300 light-years of our solar system, in whichever direction they may shine. The space agency puts its overall field of view as 400 times that of Kepler's. Rather than necessarily fixating on dim, distant stars as Kepler did, TESS studies bright, therefore close, stars 30 to 100 times as luminous as Kepler's targets.The advantage is that new generations of orbiting telescopes should be able to learn much more about the TESS exoplanets.
A year ago, TESS began examining stars in the Southern Hemisphere, aiming its four cameras to look at sections of the cosmos for 27 days straight. Each section is 24 by 96 degrees. After one of these plats undergoes the 27-day stare, TESS moves on to another.
So far, it has discovered 21 confirmed exoplanets, NASA announced on July 25. More than 850 other candidate exoplanets are awaiting confirmation.
In the first year, besides the number of detection of exoplanets and candidates, according to the agency, TESS has:
• Discovered one of the smallest exoplanets known, an object called L 98-59b, between the sizes of Earth and Mars. Another two small planets orbit the same star. This nearly doubles the number of small exoplanets that "that have the best potential" for follow-up studies to determine if they have atmospheres and what gases may make up their air, NASA said in an announcement June.
The host is a "bright, cool nearby star" designated L98-59, about 35 light-years distant. It is an M-type dwarf, a variety believed to make up three-quarters of our galaxy's stars.
• Photographed comets in our solar system.
• Discovered six supernovas in other galaxies, before their light was picked up by observers on Earth.
• Found three comets orbiting a star 63 light-years away called Beta Pictoris. The July 25 release says the comets "were too small to be planets and had detectable tails, the first identification of its type in visible light."
• Photographed "a treasure trove of astrophysical phenomena, including thousands of violently variable stellar objects," said George Ricker, TESS principal investigator, based at the Massachusetts Institute of Technology in Cambridge, quoted in the release.
"TESS has now turned its attention to the Northern Hemisphere to complete the most comprehensive planet-hunting expedition ever undertaken," the release adds. On July 18, the cameras took aim at the northern skies. "When it completes the northern section in 2020, TESS will have mapped over three quarters of the sky."