Wednesday, 12 December, 2018

First the moon outside our solar system found astronomers

Astronomers think they’ve discovered the first “exomoon” – a moon outside of our own solar system First the moon outside our solar system found astronomers
Theresa Hayes | 06 October, 2018, 23:25

The moon was discovered circling Kepler 1625b, a massive gas giant three times the size of Jupiter orbiting a star in the constellation Cygnus about 8,000 light years away, reports Sarah Kaplan at The Washington Post. The moon, which orbits a giant exoplanet called Kepler-1625b, is incredibly large, comparable to the size of the gas giant Neptune in our solar system. While astronomers now find these planets on a regular basis, the search for moons orbiting exoplanets wasn't successful - until today.

There are about 200 moons in our own solar system, including Earth's aptly named "moon".

Teachey and study co-author David Kipping, also of Columbia, were very cautious about their prospective find, emphasizing that their focus remains on confirming the existence of the exomoon around Kepler-1625b rather than musing about its potential to support life.

The candidate exomoon - signs of which were spotted by NASA's Kepler and Hubble space telescopes - may have similarly edged away from its planet over time, so it could have been much closer billions of years in the past, Kipping said. They say the first exomoon is rather unusual because of its larger size, which is comparable to the diameter of our solar system's Neptune.

Researchers analysed data from 284 Kepler-discovered planets that were comparatively in wider orbits, with periods greater than 30 days, around their host star.

"An extraterrestrial civilization watching the Earth and Moon transit the Sun would note similar anomalies in the timing of Earth's transit", Kipping said. They noticed that after Kepler-1625B crossed in front of its star there was another decrease in measurable brightness 3.5 hours late.

To find evidence for the existence of the exomoon, the team observed the planet while it was in transit in front of its parent star, causing a dimming of the starlight.

But Kepler 1625b and its moon are gaseous - not rocky - so such a collision may not lead to the condensation of a satellite. However, the researchers' alloted observation time ended before the planet could complete its transit.

In the Hubble data, they saw a moon tugging along, "trailing the planet like a dog following its owner on a leash". This shift in the planet's predicted transit was also picked up by Hubble, adding more weight to the theory that an exomoon was behind the changes. In the case of earth and sun, for example, since both bodies have mass, both exert gravitational pull on each other.

"That's been a key driver for us for a while, just trying to understand the cosmic habitats out there that we might look for, for life", says Kipping. The Earth-moon system formed as a result of a giant impact in the early solar system.

Both of these data points are best explained if a huge Neptune-sized moon is orbiting Kepler 1625b.

It's not like the exomoon in "Avatar" or Endor from "Star Wars", Teachey said, "but going forward, I think we're opening doors to finding worlds like that".

This was first observed through the Kepler telescope and then confirmed by the Hubble telescope on October 28th and 29, 2017.

In addition to this second dip in the light curve, Hubble provided compelling supporting evidence for the moon hypothesis by detecting the planet's transit more than an hour earlier than predicted.