In the last centuries it was already suspected, but until 1995, no one knew for sure that there were worlds like Earth in the orbit of other stars. Now more than 4,000 extrasolar planets are known, but still very little about their characteristics. What are they made of? How were they formed? Are they habitable? To find the answers is born Cheops, a new satellite of the European Space Agency (ESA, for its acronym in English) manufactured in Spain and focused exclusively on studying the exoplanets already identified.
Cheops It is a modest ship. It is only a meter and a half long, tall and wide, and only has one scientific instrument: a very sensitive photometer that will measure the light of other planetary systems. Its mission is to record the size of the exoplanets so that scientists can calculate the average density of each one and thus estimate its composition, that is, if they are rocky like Earth or gas balls like Jupiter and Saturn.
The mission – fast and cheap in the context of space exploration – is a milestone in ESA's scientific program. It lays the foundations for the more detailed study of exoplanets that the agency plans for the next decade, and it is also the first international space mission directed from Spain. In a competition open to European industry, the Spanish division of Airbus Defense and Space won in 2014 the contract of 25 million euros to be in charge of manufacturing the satellite. "The way it has developed has been vertigo," says Andrés Borges, the Airbus responsible for the project. Five years later, Cheops is ready to fly.
"This is the first small-scale scientific mission we carry out," said Nicola Rando, ESA project manager. Cheops, during the presentation of the satellite to the media in Airbus facilities in Madrid. He spoke next to the clean room where the device now rests under a protective cover. There it will remain until the moment of the launch arrives, programmed on board a Soyuz rocket for October of this year, from the European spaceport in French Guiana. Cheops will share the ship with another instrument of the Italian space agency, to lower the costs of this mission that the ESA has limited to 50 million euros.
When it is in Earth orbit, 700 kilometers high, the new satellite will focus its telescope on the stars of our galaxy to measure the reduction in brightness that occurs in each one when a planet crosses in front of it. This decrease in the amount of light perceived corresponds to the relative size of the planet. The great advantage of focusing on known objectives is that Cheops It will maximize the data collection during its useful life of three and a half years, since it will know exactly where to aim and when, anticipating the transit of the bodies that most interest. The repetition of stable measurements will allow, for the first time, to determine with accuracy and precision the radius of each exoplanet.
The mission is a milestone in ESA's scientific program. It lays the foundations for the more detailed study of exoplanets that the agency plans for the next decade, and it is also the first international space mission directed from Spain
In the future, a satellite equipped with a spectrograph, such as the mission Ariel programmed by ESA for the next decade, it will be able to analyze the electromagnetic spectrum of a planet to identify the chemical composition of its atmosphere, if it has one. "By the time the observations of Ariel, we will have a list of planets that we consider compatible with life as we know it, "Rando explained. Matter after the presentation.
The potentially habitable exoplanets should have a density similar to that of the Earth, and they should also be at an optimum distance from their star to avoid extreme cold or heat. However, there are bodies of other characteristics that are equally interesting for science, says Ignasi Ribas, member of the scientific team of Cheops of the CSIC and the Institute of Space Studies of Catalonia. "For example, there are many planets called hot jupiter, and we do not know why these planets exist so big that they duplicate in size to Jupiter. It is a great mystery, "says Ribas. "Also interesting planets of intermediate density between rocky and gaseous, to understand how that transition occurs," he adds.
The new mission will measure the volume of exoplanets, but it will also be necessary to know its mass in order to calculate these densities. The mass of a distant planet can be obtained by measuring the radial velocity of its star: Even with a terrestrial telescope, in many distant stars there is a slight oscillation, caused by the gravitational attraction of a planet. The oscillation causes a shift towards red or blue in the light spectrum of the star, depending on whether the planet is in front of or behind the star. This change in frequency is known as the Doppler effect; It is the same one that changes the tone of a siren when you hear an ambulance pass in the street. By knowing it, you can estimate the mass of the planet, since the most massive pull their star with more force.
ESA develops the mission Cheops in collaboration with Switzerland, with important contributions from Germany, Austria, Belgium, Spain, France, Hungary, Italy, Portugal, the United Kingdom and Sweden. 80% of the time of scientific observation will be devoted to the list of exoplanets defined by the scientific team of Cheops, while the remaining 20% will be available to scientists around the world.