Illustration: NASA

Search for ‘Earth-sized’ exoplanets

Monday 23 Apr 18


Lars A. Buchhave
DTU Space
+45 45 25 96 64


John Leif Jørgensen
Professor and Head of Measurement and Instrumentation
DTU Space
+45 45 25 34 48

Exoplanet research at DTU Space

Over the past couple of decades, we have gone from assuming that exoplanets existed to knowing that they actually do. One reason for this knowledge is the Kepler mission. 

Today, the assumption is that there are probably more exoplanets than stars in our galaxy—the Milky Way.
NASA’s TESS mission takes the next big step in the exploration of exoplanets in the Milky Way with help from DTU. The purpose of the project is to locate planets that revolve around the brightest stars and determine their atmospheric composition and size.

On the night between Monday, 16 April and Tuesday, 17 April (at 00.32, on 17 April, Danish time), another mission in which Denmark has a large share was launched from Cape Canaveral in the USA. 

This time, the mission concerns NASA’s all-sky TESS space telescope. Both DTU Space and Aarhus University participate in the mission.

TESS is scheduled to be sent into an elliptic orbit around the Earth, in which it will come close to the Moon. From here, its instruments will ‘look’ out into space in search of exoplanets. This mission aims to identify ‘interesting’ exoplanets which revolve around the brightest stars and will provide data that can be used to determine their radii.

Revolutionizing mission
On this basis, the exoplanets will subsequently be studied via telescopes from the Earth and space to characterize them. This will include determining their masses and examining their atmospheres.
“This is the next big step in the exploration of exoplanets. With the technology used, it becomes possible to search far more specifically than previously, and thus select exoplanets which it’s worth studying further. It’s a bit like looking for a needle in a haystack, but it's possible with the precision technology we use,” says Professor at DTU Space, John Leif Jørgensen.

“It's a very big American mission, in an exciting new field that will revolutionize our knowledge in this area. DTU Space has been specifically invited by NASA to participate because we have knowledge of both the science and the technology on which the mission is based.”

DTU Space has provided navigation equipment in the form of two extremely precise star trackers developed by John Leif Jørgensen’s group. They are to help ensure that the satellite is pointed in the right direction towards the universe when the planets are to be found.

"It’s a bit like looking for a needle in a haystack, but it's possible with the precision technology we use"
John Leif Jørgensen, DTU Space

New DTU research group at the forefront
The exoplanet research group at DTU Space—which is headed by Professor Lars Buch—also participates in the mission. His group is right at the forefront of the research is this field and participates in the TESS project as a partner—and by special invitation from NASA—to contribute to the project with its expertise.

“We’re moving from quantifying exoplanets to studying them more qualitatively. From previous missions, we now know that there is a huge number of exoplanets in the Milky Way. We’ll now identify those that are possible to study more closely and then start to characterize them to find out what kind of planets they are,” says Lars Buchhave.

The first exoplanet was detected in 1995. Since then, it has been established that there are thousands of them. So far, around 3,700 have been mapped , ranging from small Earth-like planets to large gas giants similar to Jupiter. One of the great future challenges will be to identify and study exoplanets which may possess the conditions required for life.

Stellar Astrophysics Centre participates from Aarhus University. With their research into exoplanets and oscillations or ‘star quakes’ in their ‘host’ stars, the Centre will be responsible for distributing the scientific data from TESS to astronomers around the world. This brings Denmark right to the centre of yet another large-scale NASA project.

TESS' vej i rummet og bane under missionen. (Illustration;: NASA)
TESS’s orbit during the mission: The pale blue ellipse shows the final orbit when the TESS satellite is in place in the trajectory from which the exoplanets are to be observed. The manoeuvre around the Moon (green and dark blue lines) ensures that TESS is raised above the Earth’s radiation belts, which would otherwise destroy TESS’s instruments. (Illustration: NASA).

Searching for exoplanets with TESS (The Transiting Exoplanet Survey Satellite)

TESS will examine a large area of the Milky Way for exoplanets which revolve around a large number of different types of stars at varying distances. The mission is a NASA project with a budget of more than EUR 134 million (DKK 1 billion) which will stretch over a number of years.

The overall goal of the mission is to detect relatively small planets approximately 1-4 times the size of the Earth that revolve around the brightest stars. TESS identifies the exoplanets by registering small changes in stellar brightness. These changes occur when a planet passes between its ‘host star’ and the line of vision of the TESS instruments.

However, the measured decrease in brightness is only an indicator, which must then be studied further to determine whether this is actually an exoplanet. Much work will thus need to be done by the exoplanet researchers to analyse the data from the mission.

The latest mission of the same nature, Kepler, identified a large number of exoplanets which revolve around relatively distant and therefore faintly shining stars very far away. Kepler examined a ‘strip’ of the Milky Way, but reached very far out into space—approximately 3,000 light years. TESS covers the whole ‘width’ of the Milky Way, but only within a ‘depth’ of approximately 200 light years, which means that especially exoplanets around brightly shining stars closer to the Earth can be identified.

The purpose of TESS is to find planets which are closer to our part of the Milky Way and which revolve around stars 30 to 100 times brighter than those observed with the Kepler mission. This makes it easier to characterize them in greater detail through follow-up missions in relation to their mass, size, density, and atmospheric conditions. Follow-ups will take place in the coming years with the James Webb telescope and other large telescopes in space and on the Earth. DTU Space participates in all these aspects of the TESS project.

TESS-instrumentet vejer ca. 362 kg og måler 1,2x1,5 m. (Illustration NASA)

TESS weighs 362 kg and measures approximately 1.2 x 1.5 m. It is launched from Cape Canaveral with a SpaceX Falcon 9 Full Thrust rocket, which is not reused. The illustration shows—among other details—the star trackers from DTU Space. (Illustration: NASA)

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25 MAY 2018