TESS: The Planet Hunter

The Transiting Exoplanet Survey Satellite (TESS) is a space telescope for NASA's Explorers program, designed to search for exoplanets using the transit method in an area 400 times larger than that covered by the Kepler mission. It was launched on April 18, 2018, atop a Falcon 9 rocket and was placed into a highly elliptical 13.7-day orbit around the Earth. The first light image from TESS was taken on August 7, 2018, and released publicly on September 17, 2018.

Over the course of the two-year primary mission, TESS is expected to ultimately detect about 1250 transiting exoplanets orbiting the targeted stars, and an additional 13,000 transiting planets orbiting additional stars in the fields that TESS observed.As of 10 May 2020, TESS has identified 1835 candidate exoplanets, of which 46 have been confirmed so far.After the end of the primary mission around July 4, 2020, data from the prime mission will continue to be searched for planets, while the extended mission will continue to acquire additional data.

The primary mission objective for TESS is to survey the brightest stars near the Earth for transiting exoplanets over a two-year period. The TESS satellite uses an array of wide-field cameras to perform a survey of 85% of the sky. With TESS, it is possible to study the mass, size, density and orbit of a large cohort of small planets, including a sample of rocky planets in the habitable zones of their host stars. TESS will provide prime targets for further characterization by the James Webb Space Telescope, as well as other large ground-based and space-based telescopes of the future. While previous sky surveys with ground-based telescopes have mainly detected giant exoplanets and the Kepler space telescope has mostly found planets around distant stars that are too faint for characterization, TESS will find many small planets around the nearest stars in the sky. TESS records the nearest and brightest main sequence stars hosting transiting exoplanets, which are the most favorable targets for detailed investigations.

TESS uses a novel highly elliptical orbit around the Earth with an apogee approximately at the distance of the Moon and a perigee of 108,000 km. TESS orbits Earth twice during the time the Moon orbits once, a 2:1 resonance with the Moon. The orbit is expected to remain stable for a minimum of ten years.Led by the Massachusetts Institute of Technology with seed funding from Google, on April 5, 2013, it was announced that TESS, along with the Neutron Star Interior Composition Explorer (NICER), had been selected by NASA for launch.

NASA's Transiting Exoplanet Survey Satellite (TESS), on July 4, finished its primary mission imaging about 75 per cent of the starry sky as part of a two-year-long survey. In capturing this giant mosaic, TESS has found 66 new exoplanets, or worlds beyond our solar system, as well as nearly 2,100 candidates astronomers are working to confirm."TESS is producing a torrent of high-quality observations providing valuable data across a wide range of science topics. As it enters its extended mission, TESS is already a roaring success" said Patricia Boyd, the project scientist for TESS at NASA's Goddard Space Flight Center in Greenbelt, Maryland.TESS monitors 24-by-96-degree strips of the sky called sectors for about a month using its four cameras. The mission spent its first year observing 13 sectors comprising the southern sky and then spent another year imaging the northern sky.Now in its extended mission, TESS has turned around to resume surveying the south. In addition, the TESS team has introduced improvements to the way the satellite collects and processes data. Its cameras now capture a full image every 10 minutes, three times faster than during the primary mission.A new fast mode allows the brightness of thousands of stars to be measured every 20 seconds, along with the previous method of collecting these observations from tens of thousands of stars every two minutes. The faster measurements will allow TESS to better resolve brightness changes caused by stellar oscillations and to capture explosive flares from active stars in greater detail.

These changes will remain in place for the duration of the extended mission, which will be completed in September 2022. After spending a year imaging the southern sky, TESS will take another 15 months to collect additional observations in the north and to survey areas along the ecliptic -- the plane of Earth's orbit around the Sun -- that the satellite has not yet imaged.TESS looks for transits, the telltale dimming of a star caused when an orbiting planet passes in front of it from our point of view. Among the mission's newest planetary discoveries are its first Earth-size world, named TOI 700 d, which is located in the habitable zone of its star, the range of distances where conditions could be just right to allow liquid water on the surface. TESS revealed a newly minted planet around the young star AU Microscopii and found a Neptune-size world orbiting two suns.In addition to its planetary discoveries, TESS has observed the outburst of a comet in our solar system, as well as numerous exploding stars. The satellite discovered surprise eclipses in a well-known binary star system, solved a mystery about a class of pulsating stars, and explored a world experiencing star-modulated seasons. Even more remarkable, TESS watched as a black hole in a distant galaxy shredded a Sun-like star.Missions like TESS help contribute to the field of astrobiology, the interdisciplinary research on the variables and conditions of distant worlds that could harbor life as we know it, and what form that life could take.

Prime mission: Searching for close-by "Earths" heading here:

TESS was first proposed in 2006 as a privately funded mission with financial backing from several institutions, including the Kavli Foundation, Google and donors at the Massachusetts Institute of Technology, according to NASA. It was eventually selected in 2013 as a mission in the Explorer program, which features large craft that do not exceed $200 million in launch costs.The mission launched on April 18, 2019, from Cape Canaveral Air Force Station in Florida aboard a Falcon 9 rocket from SpaceX. From Earth, TESS made its way to a special orbit high above the planet, where it performs observations with minimal interference from Earth's atmosphere. Weeks after its launch, it made a close pass by the moon and sent back its first test image. After three months of commissioning, TESS began searching for planets in July. The mission's stated goal is to find at least 50 planets that are close to Earth's size (no more than four times Earth's diameter).

The first planet candidate find by TESS in September 2018 was a spectacular evaporating "super-Earth" that may be made of water, or it may have a rocky core and a hydrogen and helium atmosphere. Just days later, investigators found a candidate planet slightly larger than Earth that orbits a dim red dwarf star that's only 49 light-years away from our own planet — a relatively close neighbor. Both of these finds came from examining TESS' first month of data, which was collected between July and August 2018. By early January 2019, TESS bagged its eighth confirmed planet (one that is a little smaller than Neptune) and its database of finds had hundreds of potential planetary candidates to investigate.Astrophysicists involved with the TESS mission expect the planet hunter to find more than a thousand planets smaller than Neptune and dozens of Earth-size planets, according to a 2015 paper published in the Journal of Astronomical Telescopes, Instruments and Systems. The research team stated that public data releases will happen every four months.

What do we hope will come out of the TESS mission?

The main goal is to find rocky exoplanets with solid surfaces at the right distance from their stars for liquid water to be present on the surface. These could be the best candidates for follow-up observations, as they fall within the “habitable zone” and be at the right temperatures for liquid water on their surface.TESS will use four cameras to study sections of the sky’s north and south hemispheres, looking for exoplanets. The cameras would cover about 90 percent of the sky by the end of the mission. This makes TESS an ideal follow-up to the Kepler mission, which searches for exoplanets in a fixed area of the sky. Because the TESS mission surveys the entire sky, TESS is expected to find exoplanets much closer to Earth, making them easier for further study.TESS will provide prime targets for further, more detailed studies with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes of the future.

Project timeline:

The first light image was made on August 7, 2018, and released publicly on September 17, 2018.
TESS completed its commissioning phase at the end of July and the science phase officially started on July 25. For the first two years of operation TESS monitored both the southern (year 1) and northern (year 2) celestial hemispheres. During its nominal mission TESS tiles the sky in 26 separate segments, with a 27.4-day observing period per segment.

Planet-hunting tools:

TESS occupies a never-before-used orbit high above Earth, according to NASA. The elliptical orbit, called P/2, is exactly half the moon's orbital period, which means that TESS orbits Earth every 13.7 days. Its closest point to Earth (67,000 miles, or 108,000 kilometers) is about triple the distance of geosynchronous orbit, where most communications satellites operate. When TESS reaches this point in its orbit, it transmits data to ground stations in a process that takes about 3 hours. Then TESS passes through the Van Allen radiation belts to the highest point of its orbit, at 232,000 miles (373,000 km).The solar-powered spacecraft carries four 100-millimeter-wide cameras that provide wide fields of view, according to NASA. The cameras stare at a particular region of the sky for between 27 and 351 days each, before moving on to another area. (The length of time will be decided according to where the region is in the sky, MIT said.) The spacecraft is expected to map the Southern Hemisphere in its first year, and the Northern Hemisphere in its second year.The satellite is a follow-up of NASA's highly successful Kepler space telescope, which found thousands of exoplanets during a decade of work after its launch in 2009. (Kepler ran out of fuel in 2018, but its data archive continues to be analyzed and could yield more planets). TESS, however, focuses on stars that are 30 to 100 times brighter than those Kepler examined, NASA said. It's much easier for ground telescopes to follow up on observations if the stars are bright, and easy to spot. The exoplanets TESS discovers will also be useful for the upcoming James Webb Space Telescope, which can examine the planets for more information on their atmosphere and composition, after it launches no earlier than 2021.Like Kepler, TESS examines variations in the brightness of stars. If an exoplanet passes in front of a star (called a planetary transit), it blocks a portion of the light and causes the brightness to dip. The mission is expected to collect thousands of candidate exoplanets, including Earth-sized and "super-Earth-size" planets. This will help astronomers better understand the structure of solar systems outside of our Earth, and provide insights into how our own solar system formed.

How TESS works:

TESS is surveying an area in the sky that is 400 times larger than what Kepler observed, including 200,000 of the brightest nearby stars. Over the course of two years, the four wide-field cameras on board will stare at different sectors of the sky for days at a time. This will enable scientists to survey nearly the entire sky.These findings are from just the first few sectors TESS has observed in the Southern Hemispheres, beginning in July.TESS will look for exoplanets using the transit method, observing slight dips in the brightness of stars as planets pass in front of them. Bright stars allow for easier followup study through ground- and space-based telescopes.
NASA expects TESS to allow for the cataloging of more than 1,500 exoplanets, but it has the potential to find thousands. Of these, officials anticipate, 300 will be Earth-size exoplanets or double-Earth-size Super Earths. Those planets could be the best candidates for supporting life outside our solar system. Like Earth, they are small, rocky and usually within the habitable zone of their star, meaning liquid water can exist on the surface.TESS is considered to be a "bridge to the future," These exoplanets will be studied so that NASA can determine the best targets for future missions, like the James Webb Space Telescope. That telescope, launching in 2021, would be able to characterize the details and atmospheres of exoplanets in ways scientists have not been able to do.Scientists are already working on followup observations for more than 280 planet candidates that TESS has found.

Result:

On January 6, 2020, NASA reported the discovery of TOI 700 d, the first Earth-sized exoplanet in the habitable zone discovered by the TESS. The exoplanet orbits the star TOI 700 100 light-years away in the Dorado constellation. The TOI 700 system contains two other planets: TOI 700b, another Earth-sized planet and TOI-700c, a super-Earth. This system is unique in that the larger planet is found between the two smaller planets. It is currently unknown how this arrangement of planets came to be, whether these planets formed in this order or if the larger planet migrated to its current orbit.On the same day NASA announced that astronomers used TESS data to show that Alpha Draconis is an eclipsing binary star.The same day, the discovery of TOI 1338 b was announced, the first circumbinary planet discovered with TESS. TOI 1338 b is around 6.9 times larger than Earth, or between the sizes of Neptune and Saturn. It lies in a system 1,300 light-years away in the constellation Pictor. The stars in the system make an eclipsing binary, which occurs when the stellar companions circle each other in our plane of view. One is about 10% more massive than our Sun, while the other is cooler, dimmer and only one-third the Sun's mass. TOI 1338b's transits are irregular, between every 93 and 95 days, and vary in depth and duration thanks to the orbital motion of its stars. TESS only sees the transits crossing the larger star — the transits of the smaller star are too faint to detect. Although the planet transits irregularly, its orbit is stable for at least the next 10 million years. The orbit's angle to us, however, changes enough that the planet transit will cease after November 2023 and resume eight years later.

Scaling the Heights:

Pre Q: TESS orbits earth every

(a) 12 hrs
(b) 24 hrs
(c) One day
(d) 13.7 day

Mains Q: What are the objectives of TESS mission? What is the difference between TESS and Kepler spacecraft? Discuss briefly its future prospects.