Rendering of part of a planetary system in orbit around a white dwarf star (the white spot at the center of the red ring). The foreground shows rocky asteroids; the red ring represents the rocky debris that remains of former asteroids or a minor planet that have already been broken apart by the strong gravity of the white dwarf. Credit: University of Warwick
Object in the constellation Boötes with C, H, O, N. Many scientists believe the Earth was dry when it first formed, and that the building blocks for life on our planet – carbon, nitrogen and water – appeared only later as a result of collisions with other objects in our solar system that had those elements. Today, a UCLA-led team of scientists reports that it has discovered the existence of a white dwarf star whose atmosphere is rich in carbon and nitrogen, as well as in oxygen and hydrogen, the components of water. The white dwarf is approximately 200 light years from Earth and is located in the constellation Boötes.
Although the study focused on star WD 1425+540 – the fact that its planetary system shares characteristics with our solar system strongly suggests that other planetary systems would also. “The findings indicate that some of life’s important preconditions are common in the universe,” Zuckerman said. A minor planet in the planetary system was orbiting around the white dwarf, and its trajectory was somehow altered, perhaps by the gravitational pull of a planet in the same system. That change caused the minor planet to travel very close to the white dwarf, where the star’s strong gravitational field ripped the minor planet apart into gas and dust. Those remnants went into orbit around the white dwarf — much like the rings around Saturn before eventually spiraling onto the star itself, bringing with them the building blocks for life.
The researchers think these events occurred relatively recently, perhaps in the past 100,000 years or so. They estimate that approximately 30% of the minor planet’s mass was water and other ices, and approximately 70% was rocky material. The research suggests that the minor planet is the first of what are likely many such analogs to objects in our solar system’s Kuiper belt beyond Neptune.
White dwarf stars are dense, burned-out remnants of normal stars. Their strong gravitational pull causes elements like carbon, oxygen and nitrogen to sink out of their atmospheres and into their interiors, where they cannot be detected by telescopes. This is the first time a white dwarf with nitrogen has been discovered, and one of only a few known examples of white dwarfs that have been impacted by a rocky body that was rich in water ice.
Siyi Xu, a postdoctoral scholar at the European Southern Observatory in Germany said. “If Earth obtained its water, nitrogen and carbon from the impact of such objects, then rocky planets in other planetary systems could also obtain their water, nitrogen and carbon this way.”
A rocky planet that forms relatively close to its star would likely be dry. “We would like to know whether in other planetary systems Kuiper belts exist with large quantities of water that could be added to otherwise dry planets,” he said. “Our research suggests this is likely.”
According to Zuckerman, the study doesn’t settle the question of whether life in the universe is common. “First you need an Earth-like world in its size, mass and at the proper distance from a star like our sun,” he said, adding that astronomers still haven’t found a planet that matches those criteria.
The researchers observed WD 1425+540 with the Keck Telescope in 2008 and 2014, and with the Hubble Space Telescope in 2014. They analyzed the chemical composition of its atmosphere using an instrument called a spectrometer, which breaks light into wavelengths. In the new study, the researchers saw the elements in the white dwarf’s atmosphere because they absorbed some of the background light from the white dwarf. http://newsroom.ucla.edu/releases/dwarf-star-200-million-light-years-away-contains-lifes-building-blocks
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