New planet search around Alpha Centauri – space telescope with diffractive lens to detect gravitational tumbling of stars –

Does our neighboring system Alpha Centauri also have planets? So far the answers to this have been contradicting itself. Therefore, a special space telescope is now to search for exoplanets around the double star, which is only four light-years away. The diffraction lens system of the telescope, called “Toliman”, is supposed to capture the tiny tumbling movements that the gravity of a planet triggers in the stars. The start is planned for 2023.

They are our closest stellar neighbors: the red dwarf Proxima Centauri and the two sun-like stars of Alpha Centauri are only a good four light-years away from us. They would therefore be the most promising and immediate targets for a future interstellar mission. Two planets have already been discovered around Proxima Centauri, but these are hit by strong bursts of rays from their star. More promising candidates for a “second earth” would therefore be planets around the quieter stars of Alpha Centauri.

Alpha Centauri in an image taken by the Hubble Space Telescope. © NASA/ESA

Planetenfahnder „Toliman“

But despite an intensive search, astronomers at Alpha Centauri have not yet found anything – at least not clearly. An instrument specially installed on the Very Large Telescope (VLT) of the European Southern Observatory in Chile recently discovered a suspicious infrared heat spot around Alpha Centauri A. If this signal comes from a planet, it could be about the size of Neptune and just within the star’s habitable zone.

The Toliman mission could clarify whether it is really a planet and whether there are perhaps other planetary satellites around Alpha Centauri. The name Toliman stands on the one hand for the Arabic name of Alpha Centauri, on the other hand it is the abbreviation for “Telescope for Orbit Locus Interferometric Monitoring of our Astronomical Neighborhood”. It is a space telescope whose optics are specially designed for the search for planets near our neighboring stars.

Stellar “tumbling” as an indication

“The Toliman Mission will be a big step in resolving whether there are habitable planets there,” said Pete Worden, executive director of the Breakthrough Initiatives. Together with NASA’s Jet Propulsion Laboratory, the University of Sydney and Saber Astronautics, they want to put the Toliman space telescope into orbit as early as 2023. “Our plan is an agile, low-cost mission that will start delivering results by the middle of this decade,” says Peter Tuthill of the University of Sydney.

Toliman is not supposed to detect the exoplanets using the transit method or other signals that are directly visible in the visible or infrared range. Instead, the astronomers want to find potential planets around Alpha Centauri using their gravitational effects. The gravitational pull of the planets causes tiny irregularities in the rotation and movement of their central stars, which could be discernible in the light spectrum through spectral shifts.

Planned construction of the Toliman telescope and its lens. © Peter Tuthill/ University of Sydney

A more precise view thanks to diffractive optics

However, the Toliman telescope has a special feature: To make the subtle tumbling of the stars more visible, it has a diffractive lens – a lens with a corrugated fine structure that breaks and intensifies the light in a special way – similar to the Fresnel lenses of a lighthouse. Such optics do not produce a clear image of the stars, but are particularly suitable for showing irregularities in the movement of the stars, as the team explains.

“The signal we’re looking for takes a real leap in the accuracy of the measurements,” says Pete Klupar, chief engineer at Breakthrough Watch. The astronomers hope that the new system will bring this additional resolution. “Neither of us underestimates the challenge, but our innovative design involves a few tricks,” says Tuthill. According to the researchers, their technology is particularly well suited to tracking down exoplanets in the habitable zone of the stars.

Next target for interstellar missions

“Knowing our closest exoplanetary neighbors is extremely important,” says Tuthill. “Because these planets are the ones where we have the best chances of finding and analyzing atmospheres, exploring surface chemistry and maybe even discovering biosignatures of life.” Klupar adds: “These nearby planets will also be the first targets. which will steer humanity with its first steps in the interstellar space. “

The Breakthrough Initiative is already planning to send unmanned mini-probes to Alpha Centauri using light sails. The radiation pressure from lasers is supposed to provide the necessary thrust at take-off, the rest is then done by sunlight. The first tests of such light sail probes in Earth orbit have already taken place.

Quelle: Breakthrough Initiatives, University of Sydney

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