Alien stars could send comets crashing through the inner solar system
A new study using data from ESA's Gaia satellite has tracked the movement of more than 300,000 stars relative to the Sun, and discovered that some will pass close enough to disturb the vast cloud of comets that make up the Oort Cloud. These comets could pass close to – or even strike – the Earth at some point in the distant future.
The Gaia satellite was launched in December 2013 atop a Soyuz-STB/Fregat-MT on a five-year primary mission to create the largest and most accurate three-dimensional map of our galaxy to date, by surveying over a thousand million stars.
To achieve this, the satellite was fitted with two rectangular optical telescopes, which work in conjunction with three scientific instruments to determine the location of stars, the characteristics of their light, and their velocities and movement.
The first 14 months of Gaia data containing information on over a billion stellar bodies was released back in September 2016.
For the new study, scientists took details on the positions, proper motion and parallax motions of over 300,000 stars from Gaia's initial data release, and combined it with the radial velocities of the same stellar bodies that were contained in a separate star catalogue.
With this information, the team determined the closest approach of the stars to our Sun for up to five million years in the past, and the same amount of time into the future.
By working out the distance at which a star will pass by our solar system, the astronomers were able to ascertain the number of stellar bodies capable of disturbing the Oort Cloud, and sending comets racing into the inner solar system.
The Oort cloud is a humongous sphere of icy debris and comets located roughly 15 trillion km from the Sun, and is thought to be the point of origin for many long-period comets, such as Siding Spring, which passed within 87,000 miles (139,500 km) of Mars in October 2014.
The scientists behind the new research believe that, depending on its mass, a star would have to pass within roughly 60 trillion km of the Sun for its gravitational influence to tug at the mass of comets.
It was discovered that 97 stars will pass within 150 trillion km of the Sun. Sixteen will pass closer than 60 trillion km, meaning that they could potentially disturb the Oort Cloud, and one – a star known as Gliese 710, will actually pass through it.
Gliese 710 is a well-known K dwarf star roughly 61 percent the mass of our Sun. An older pre-Gaia release estimate of the star's motion stated that Gliese 710 was likely to pass within 3.1 – 13.6 trillion km of the Sun. However, the latest study asserts that, in about 1.3 million years, the star will likely pass within 2.3 trillion km, or even as close as 1.5 trillion km of the Sun.
At its closest, Gliese 710 will be the brightest object in the night's sky, and, moving at an estimated speed of 50,000 km/h (31,000 mph), roughly half the speed of the average close proximity star, will have plenty of time to wreak havok with the Oort Cloud before passing.
The study also made an estimate of the rate of close encounters we can expect in the past five million years, and the next five million, while using a computer model to factor in stars that have not yet been observed and catalogued.
It was estimated that the solar system would experience 550 stellar flybys during each million-year period passing within 150 trillion km of the Sun. Twenty of these would pass within 30 trillion km.
A paper detailing the research has been published in the journal Astronomy & Astrophysics.
Scroll down to see a video displaying the motions of nearby stars 1.1 – 1.5 million years in the future. The trajectory of Gliese 710 is displayed as a white line.