Hunting for Planets with Plato

Categories: Also in News Missions

New mission will hunt for Sun-Earth systems

The five Lagrangian points for the Sun-Earth system are shown in the diagram above. An object placed at any one of these 5 points will stay in place relative to the other two. Credit: NASA

The European Space Agency has announced the selection of the Planetary Transits and Oscillations of stars (PLATO) mission as part of the Cosmic Vision 2015–25 Programme. According to ESA, the mission will address themes of the Cosmic Vision that include, "what are the conditions for planet formation and the emergence of life" and "how does the Solar System work?"

The mission will be composed of 34 separate small telescopes and cameras, which will rest in the L2 Langrangian points 1.5 million kilometers from Earth. Lagrangian points are positions in space relative to the Earth and the Sun where a small object is affected by the gravity of the two larger objects in such a way that it remains in a constant-pattern with the planet. Basically, the combined gravitation pull of the Earth and Sun will keep PLATO positioned in the same spot relative to Earth indefinitely. Earth’s second Lagrangian point (L2) sits behind the Earth relative to the Sun.

From this vantage point, scientists hope PLATO will identify thousands of planetary systems around up to a million stars. The focus of the mission is to identify systems similar to our own, with Earth-sized and super-Earth planets orbiting within their host star’s habitable zone. PLATO will also be capable of studying seismic activity in stars, providing astrobiologists with details about a star’s age as well as its mass and radius.

Artist impression of two spacecraft concepts for the PLATO mission that were studied during the assessment phase: (left) concept from Thales Alenia Space, and (centre) concept from EADS Astrium. Credit: ESA

Alvaro Giménez, Director of Science and Robotic Exploration at ESA, said in a recent press release, "PLATO, with its unique ability to hunt for Sun–Earth analogue systems, will build on the expertise accumulated with a number of European missions, including CoRot and Cheops."

ESA is looking to launch PLATO sometime in 2022-2024, and the mission will be complimented by ground-based observations and data from ESA’s recently-launched Gaia mission. Together, the information provided by these missions could allow astrobiologists to determine characteristics of extrasolar planets that affect their potential to support life. This includes the planets’ radii, densities, and the amount of stellar irradiation they experience.

PLATO is scheduled to operate for at least six years for its primary mission.

ESA has selected two other missions alongside PLATO – the Solar Orbiter and Euclid. Solar Orbiter will study the Sun and features like the solar wind. Euclid will collect data about the structure of the Universe, including detailed studies of dark matter and dark energy.

Astrobiology Magazine (AM) contacted Dr. Don Pollacco with some questions about the upcoming Plato Mission. Pollacco is the Science Coordinator for PLATO and a Professor in the Astronomy and Astrophysics Group at the University of Warwick.

AM: What are some benefits of building the mission with 34 separate telescopes rather than a single, large mirror?

Professor Don Pollacco of the University of Warwick. Image Credit: University of Warwick

Dr. Pollacco: For any telescope field of view, you always see more faint stars than bright stars. To study small planets in any detail (or even confirming they are indeed planets) requires their host stars to be relatively bright and nearby. If you take the NASA Kepler mission for example, many (>>90%) of the candidate planets are well beyond confirmation. Doing other experiments such as analysing their atmospheres is pretty much impossible. To see lots of bright stars you need short focal length instruments, hence the resemblance to a compound eye.

This concept has other advantages such as bright stars can be studied with data from just a single camera while data from several cameras can be combined for fainter stars (mimicking a larger telescope). The other great advantage is that the cameras can be offset in the the sky (plato uses 4 groups of 8 cameras for example), to enable a much larger part of the sky to be observed.

Cameras can be tasked to work at different wavelengths – in principle this can give you atmospheric information.

Finally there is redundancy. If one or two cameras break down you don’t loose the experiment.

AM: How much detail do you expect PLATO to return about extrasolar atmospheres?

Dr. Pollacco: See above, but more importantantly it will find the targets that can be used for a real survey of HZ [habitable zone] terrestrial planet atmospheres.

AM: What stage of development is PLATO in?

Dr. Pollacco: Unfortunately the timescale is dictated by external factors e.g. funding profile, manufacture of parts (e.g. ccd’s and optics). Launch is scheduled for the 2022-24 slot (the ESA M3 slot). However, the technology is relatively mature and there are few risks (relative to other missions anyway!).

PLATO is the logical next step – it will explore and characterise HZ planets and lead to a far better understanding of the earth in space and give the best sample for a systematic search for life.


PLATO – A mission to search for other Earths. Credit: Astronomical Observatory of Padova (YouTube)