Rocky Tatooine-like exoplanets could exist after all
An international team of scientists may have discovered debris from a metal-rich, rocky asteroid falling into a white dwarf that comprises one half of a distant binary star system. The presence of the asteroid suggests that rocky, and potentially habitable worlds could potentially form in a two-star system, not entirely unlike the fictional planet Tatooine on which Luke Skywalker was raised in the Star Wars universe.
Prior to the recent observations, it had been thought that the focus of the study, the solar system SDSS 1557, was centered around a single white dwarf star. However, upon closer observation the team was able to discern the presence of a second brown dwarf star, whose gravity was pulling on its larger neighbor.
Ordinarily, in a single-star system, the planetary and sub-planetary bodies would form incredibly slowly from the material left over from the creation of the central star. The gravity of the new-born star would sculpt this material into what is known as a protoplanetary disk. Over time, particles of dust and other materials would collide to form larger and larger chunks of matter, and from these minuscule beginnings a planet could be born.
However, it was thought that in a dual-star system, things may not be so simple. Prior to the new study, only gas giants, such as Jupiter or Saturn, had been discovered in double-star systems, leading astronomers to assume that the chaotic push and pull of the gravity of the duelling stars was stopping the rock and dust from coalescing and growing into rocky planets.
Owing to the fact that the SDSS 1557 System lies some 1,000 light-years distant from Earth, and that the asteroid from which the debris originated was thought to be only 4 km (2.5 miles) in width, it would be impossible to have directly imaged its remains.
However, by using the ESO's Very Large Telescope in concert with the Gemini Observatory South telescope, both of which are located in Chile, the team was able to observe the light signature of the material as it was drawn from its orbit and onto the surface of the white dwarf star. By measuring the light absorption of specific light wavelengths as this event unfolded, the team was able to deduce the chemical composition of the ex-asteroid.
It was found that the rocky debris had a high metal content, and boasted an abundance of both silicon and magnesium, unlike the icy carbon-rich material detected in other binary systems.
Asteroids in orbit around our sun are considered to be near-perfect time capsules that allow scientists to observe the building blocks of our solar system, and the same holds true for their counterparts in orbit around distant stars. The researchers believe that by analyzing the light signature of the debris, they can gain a greater understanding of how rocky planets could come to form under the gravitational influence of dual stars.
The team believes that roughly 1.1 trillion tonnes of material collided with the surface of the star over the course of the event, and it is likely that, unless further debris is drawn to its surface, the newly-deposited metals will sink down into the star and disappear in a few weeks. The next step for the team will be to use the powerful Hubble Space Telescope to confirm that the asteroid was indeed composed of a rocky material as the new research suggests, rather than ice, which is more commonly found in binary star systems.
Should the follow-up observations corroborate the team's findings, it will serve as a strong indicator that the formation of rocky planets is possible in a binary system, despite the tumultuous gravitational influence of the double stars.
Source: University College London