New laser tech may help find Earth-like planets

A new laser-based technology may help discover Earth-like exoplanets orbiting distant stars in the near future, scientists say.
Astronomers want to rediscover Venus using a new powerful optical device installed on the Italian National Telescope that will measure the planet's precise gravitational pull on the Sun.
If successful, the first-of-its-kind demonstration of this new technology will be used for finding Earth-like exoplanets orbiting distant stars, researchers said.
"We are building a telescope that will let us see the Sun the way we would see other stars," said Chih-Hao Li, a staff scientist at the Harvard-Smithsonian Centre for Astrophysics.
Astronomers have identified more than 1,700 exoplanets, some as far as hundreds of light years away.

Most were discovered by the traditional transit method, which measures the decrease in brightness when a planet orbiting a distant star transits that luminous body, moving directly between the Earth and the star. This provides information about the planet's size, but not its mass.

Li and Phillips are developing a new laser-based technology known as the green astro-comb for use with the "radial velocity method," which offers complementary information about the mass of the distant planet.
From this information, astronomers will be able to determine whether distant exoplanets they discover are rocky worlds like Earth or less dense gas giants like Jupiter.

The method is precise enough to help astronomers identify Earth-like planets in the "habitable zone," the orbital distance "sweet-spot" where water exists as a liquid.
The radial velocity method works by measuring how exoplanet gravity changes the light emitted from its star. As exoplanets circle a star, their gravitation tugs at the star changing the speed with which it moves toward or away from Earth by a small amount.
The star speeds up slightly as it approaches Earth, with each light wave taking a fraction of a second less time to arrive than the wave before it.
To an observer on Earth, the crests of these waves look closer together than they should, so they appear to have a higher frequency and look bluer, researchers said.

As the star recedes, the crests move further apart and the frequencies seem lower and redder.
This motion-based frequency change is known as the Doppler shift. Astronomers measure it by capturing the spectrum of a star on the pixels of a digital camera and watching how it changes over time.
Today's best spectrographs are only capable of measuring Doppler shifts caused by velocity changes of 1 meter per second or more. Only large gas giants or "super-Earths" close to their host stars have enough gravity to cause those changes, researchers said.
The new astro-comb Li, however, will be able to detect Doppler shifts as small as 10 centimetres per second - small enough to find habitable zone Earth-like planets, even from hundreds of light years away.