NASA's TESS spacecraft completed its main mission about three months ago. The task of TESS (Transiting Exoplanet Survey Satellite) was to search the brightest stars near Earth for transit exoplanets. 74 confirmed exoplanets were found, with an additional ~ 1200 candidates awaiting confirmation.
During its two-year main mission, 75% of the sky was measured. Now NASA has released a composite image of the northern sky that consists of more than 200 individual images.
To accomplish its task, TESS divided the northern sky into 13 separate, manageable sectors. It monitored every sector with its four cameras for nearly a month, looking for the tell-tale darkening of the stars when a planet passes in front of it.
This northern sky mosaic contains 208 images captured by NASA's Transiting Exoplanet Survey Satellite (TESS) during its second year of scientific operations, which concluded in July 2020. bright white oval in the middle left in the picture.
It took almost a full year of images to create the panorama of the northern sky, just as it did the southern panorama that NASA released about a year ago.
The northern panorama has some significant gaps compared to the more complete southern panorama. In a press release, NASA explains: “For about half of the northern sectors, the team decided to point the cameras further north to minimize the effects of stray light from the earth and moon. This leads to a significant gap in reporting. "
The southern sky panorama from TESS was released about a year ago. It is a more complete picture than the panorama of the northern sky. It shows the striking Milky Way, the Orion Nebula above and the large Magellanic Cloud in the middle. Photo credit: NASA / MIT / TESS and Ethan Kruse (USRA)
These panoramas are just a side effect of TESS. They're interesting and cool, but they're only a tiny fraction of the data stream that the spaceship sent back to Earth. TESS has four cameras, but there's a lot more to it than that.
Each of the four cameras has four CCD sensors (Charge Coupled Device) for a total of 16. During the two-year duration of its main mission, TESS imaged one of the 13 sky sectors every 30 minutes. Each TESS CCD has taken over 30,000 complete scientific images. If you combine all of this imagery with the other data that TESS sends to Earth, the spaceship has sent back more than 40 terabytes of data so far. According to the press release, this is "… synonymous with streaming around 12,000 high-resolution films".
According to NASA, this flood of data is just the beginning. TESS has now started its secondary mission where it will spend another year recreating the southern sky. It will search the parts of the sky it missed last time and take a second look at some planetary candidates.
NASA has made some improvements to the way TESS collects and manages its data. The spaceship will now map every sector of the sky in just 10 minutes instead of the previous 30 minutes. It can also measure the brightness of thousands of stars every 20 seconds. So during the secondary mission, TESS will provide a lot more data. In this case, more data means a more successful mission.
TESS has a unique, 13.7 day, highly elliptical cislunar orbit around the earth. With an observation period of 27.4 days per segment, the satellite is most sensitive to exoplanets with a period of less than 13 days (so at least two transits are used for the discovery).
The circular areas in which segments overlap at the ecliptic poles have an observation period of just over 100 days, which allows planets with longer periods to be discovered. These regions are called Continuous Viewing Zones (CVZs). Photo credit: TESS / MIT
"These changes promise to make TESS's expanded mission even more fruitful," said Padi Boyd, project scientist for the mission at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Highly accurate measurements of star brightness at these frequencies make TESS an exceptional new resource for studying flaming and pulsing stars and other transient phenomena, as well as for researching the science of exoplanet transit."
TESS's sensitive instruments found more than just exoplanets during their main mission. The spaceship also found a black hole in the destruction of a star, an eruption of Comet 46P / Wirtanen, and helped astronomers understand a bizarre type of pulsating star.
And TESS also has a guest investigator program. It runs on annual cycles, and during each cycle there are approximately 200,000 targets that GIs can apply to review. Each proposal selected grants a 2-minute and 20-second “cadence stamp” for a single goal. During the two years of its main mission, TESS granted guest investigators around 20,000 of these opportunities.
An artistic illustration of TOI 700d, an earth-sized exoplanet that TESS found in the habitable zone of its star. Photo credit: NASA
TESS was a very successful mission in almost every way. It was recorded where NASA's Kepler Observatory left off in October 2018 after more than 2,500 exoplanets were discovered. But while Kepler was sent into space to find possible exoplanets, TESS's mission is refined and based in part on Kepler's success.
Kepler found many gas giants and hot Jupiters, as well as planets unsuitable for life. However, TESS has a more specific goal: to discover Earth- and Neptune-sized planets orbiting stable stars that don't have much flare. When the mission was designed and launched, NASA expected TESS to discover more than 20,000 transit exoplanets, including 500 to 1,000 Earth-sized planets and super-earths. It has been largely successful so far.
TESS focuses on near-Earth stars that are better suited for follow-up observations. The James Webb Space Telescope will be able to examine exoplanet atmospheres for biosignatures, and ESA's CHEOPS mission to characterize exoplanet satellites is currently in operation. The task is to estimate the mass, density, composition and formation of exoplanets.
Thanks to TESS, follow-up observations are much easier. While Kepler catapulted our understanding of exoplanets into the future with his raw power and found exoplanets at great distances, TESS is different. By focusing on closer exoplanets, it makes its own massive contribution to our burgeoning knowledge of exoplanets.