Launch expected today: NASA's space telescope TESS

The launch of Transiting Exoplanet Survey Satellite (TESS), better known as TESS, is now set for Wednesday, April 18 at 6:51 p.m. EDT. The space probe is powerful.

Its four cameras will monitor the 200,000 brightest stars in the vicinity of our sun, and, as with its predecessor telescope, Kepler, NASA scientists hope to find thousands of exoplanet candidates and to also confirm many of those as genuine.

About 300 of them, NASA estimates, may turn out to be about the size of our Earth.

For astronomers it has been incredibly difficult to find exoplanets. In contrast to the stars they circle, they do not emit their own light or radiation and usually stay in the dark – almost impossible to detect with optical telescopes.

Furthermore, being in far away galaxies, they are unbelievably tiny from the perspective of Earth.  

Such exoplanets only give a hint about their existence when they transit in front of their respective sun – from the perspective of Earth. They then cast a shadow and, for the time of their transit, the light emitted from their star gets somewhat dimmer.

The change in the light, the time it takes and the frequency with which such darkening occurs give astronomers important information that they can use to compute the characteristics of the planet: Its size its orbit and the distance from the planet. 

The predecessor

NASA already used this physical method with its satellite Kepler between 2009 and 2013. The space probe observed 150,000 stars permanently and registered the slightest light fluctuations.

The satellite focused on a rather narrow section of the Milky Way located in the constellations of Cygnus, Lyra and Draco. At the end of the three-and-a-half year mission, Kepler had found more than 5,000 new candidates for exoplanets and actually confirmed the existence of half of them.

Read more: NASA finds more Earth-sized planets that could support life

Due to technical problems, though, the Kepler mission later had to be refined. From 2014 on the spacecraft, under the mission name K2, searched through a larger section of the skies for different celestial bodies and events, such as supernova explosions, star systems, asteroids and comets.

Even then, Kepler still managed to find more exoplanets.

Now, Kepler is finally running out of fuel. This, in addition to other technical difficulties, is one of the reasons NASA opted to launch its successor, TESS.

Small satellite, big expectations

This new satellite is expected to deliver data for two years. Its range of observation is 400 times larger than that of Kepler, and in contrast to its predecessor, TESS will not always be looking at the same section of the sky: It divides the heavens into 26 sectors. The craft will monitor each of those sectors for 27 days.

And TESS can do even more. Astronomers from universities as well as other partners have had the opportunity to list about 20,000 other celestial objects that TESS will take a look at - and about which it will deliver more up-to-date data.

At the end of this year, the European Space Agency (ESA) is planning to launch the Characterizing ExoPlanets Satellite (CHEOPS). It will be equipped with only one telescope and will be positioned in a sun-synchronous orbit, meaning that it will fly around the Earth in such a way that the sun – from the perspective of the space probe – is always in the same place.

Unlike TESS, the primary task for CHEOPS will not be to search for more exoplanets. Rather, it is going to look into already known exoplanets to measure them more precisely than ever before.