Earth analog search is boosted by new telescope

Earth analog search is boosted by new telescope

An Earth-like planet with a sun-like star is the holy grail of planet hunters. An Australian astronomer is searching for him using a special new space telescope.

Does Earth’s twin brother orbit the nearest star? It can just be. And if that’s the case, Peter Tuthill wants to find him. Earlier this month, an Australian astronomer presented plans for a small but very special space telescope looking for an Earth-like planet orbiting Alpha Centauri, the star closest to the sun.

Our Earth is one of the eight planets revolving around the sun. But for a quarter of a century, astronomers have known that most other stars are also accompanied by planets. More than 5,000 of these “exoplanets” have already been discovered, primarily around faint small dwarf stars, where they are easy to find.

The Holy Grail of planet hunters is of course a true twin brother of Earth: a small, rocky planet orbiting a star very similar to the Sun. And then at just the right distance, so that water and life can happen on the surface. No such “Earth 2.0” was found.

Small changes in the intentionally out-of-focus image of binary star Alpha Centauri could reveal the presence of an Earth-like planet.University of Sydney’s photo

Tuthill hopes to acquire Alfa Centauri soon. Its Toliman Space Telescope (Toliman was the old Arabic name for the star) should be able to detect an Earth-like planet in the “habitable zone” around this closest neighbor to the Sun.

binary star system

It’s a wild guess, he knows it. Alpha Centauri is a binary star: two stars that orbit each other once every 80 years, in a wide elliptical orbit. It is unclear whether planets can form in such a binary star system as easily as planets form around a single star like the Sun. (A planet was actually found in 2016 near Proxima Centauri, a dwarf star orbiting the binary at a much greater distance.)

However, it’s definitely worth looking for, according to exoplanet researcher Aurora Keseli of the Leiden Observatory. Ideally, astronomers would like to photograph other planets and take measurements of atmospheric composition. “It’s not really a distant future anymore,” Kessely says. This of course works best if the planet isn’t too far away, so Alpha Centauri, at a distance of “only” 4.4 light-years (more than 40 trillion km), is an ideal target. “This is the first step.”

For this first step, the University of Sydney is partnering with NASA’s Jet Propulsion Laboratory, Australian space company Saber Astronautics and investor Yuri Milner on the breakthrough initiatives, which are also developing future plans for an entire fleet of Alpha Centauri system microsatellites. “We are still looking for additional funding, but the project will definitely go forward,” Tuthill says.

small swing

It’s not easy. An orbiting planet pulls on its parent star with its gravity. Even if you can’t see the planet itself, you can infer its existence from the star’s small periodic oscillations. Normally you would measure this in relation to the stars in the background, but in this case that doesn’t provide the required accuracy.

Instead, the Toliman Space Telescope precisely measures the distance between the two brightest stars in a binary star system. If there are no planets, these two stars describe gentle even elliptical orbits around their common center of gravity. But if there is an Earth-like planet orbiting one of them, there must be little additional oscillation.

Measured on a telescope detector, this is an aberration less than the diameter of an atom, according to Tuthill’s calculation. Oddly enough, the only way to measure this is to deliberately show the two stars “out of focus”. The carefully designed pattern of microscopic “scratches” on the telescope’s mirror results in a subtle, almost fan-shaped image of the binary star, with many sharp peaks. Even with the slightest difference in the distance between the two stars, the resulting image will look slightly different.


Similar techniques were developed in Leiden by David Doelman and colleagues. Doelman has already collaborated with Tuthill on an earlier project, and so Leiden astronomers have engaged in a little “introduction” to the Toliman mission: a technical test aboard the Cuava-1 small satellite, which was launched last summer. Unfortunately, this ended badly: no radio signals were ever received from the satellite.

But the technology itself works well, says Doelman: “Everything has been extensively tested in the lab.” It remains uncertain whether Leiden liquid crystal technology will also be used in Tollman’s final mission.

So there is more uncertainty. Who will provide the parts for a small space telescope, for example. Whether there is soon enough financial room to upgrade – in Tuthill’s words – “from Volkswagen to Mercedes”. Which rocket would be used to put the Toliman into orbit. And whether he will stay with the search in Alpha Centauri.

“Our method only works with double stars,” Tuthill explains. “Other interesting binary stars are much further away, which makes measurements more difficult, but who knows, it may be possible to track more massive planets out there – the so-called super-Earths.”

This is all accidental. What matters is that intriguing “second Earth” that astronomers have been searching for for so long that could be right around the corner. “I expect to start in 2026,” Tuthill says. “It should be clear within two years whether this planet really exists.”

An image of the binary star Alpha Centauri taken by the Hubble Space Telescope.  Photo by ESA/Hubble & NASA

An image of the binary star Alpha Centauri taken by the Hubble Space Telescope.Photo by ESA/Hubble & NASA

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