The University Record, June 7, 1999

Scientists calculate odds of doomsday scenarios for the solar system’s fate

By Sally Pobojewski
News and Information Services

“Some say the world will end in fire.

Some say in ice.” --Robert Frost

For a poet, Robert Frost was a pretty good scientist, say astrophysicists Fred Adams and Greg Laughlin. Frost’s fire-or-ice scenario neatly sums up two outcomes from their new study of possible future encounters between our solar system and passing stars.

While other astrophysicists study how the universe began, Adams and Laughlin are fascinated by how it will end. In a presentation at the American Astronomical Society meeting in Chicago last week, Adams presented their apocalyptic visions of what could happen to our solar system in the next 3.5 billion years.

Laughlin and Adams used a computer and statistical processing calculations to model more than 200,000 interactions between binary stars passing by our solar system and orbits of the Earth, sun and four outer planets, especially Jupiter.

“Jupiter is vulnerable to gravitational interactions with a passing star,” says Adams, associate professor of physics. “Because of its large mass, even a modest disruption of Jupiter’s orbit could have a catastrophic effect on Earth. The chances of such an encounter either hurling the Earth out into space or plunging it into the sun during the next 3.5 billion years are about one in 100,000—much greater than your chances of winning the Michigan lottery.”

Other possibilities and their estimated odds of occurrence include: Doubling of the eccentricities of Neptune’s orbit (one in 400), Earth being directly ejected from the solar system by a passing star (one in 2.2 million), Earth being captured by a passing star (one in 3.6 million), and the solar system capturing another star (one in 300,000).

Without one of the escape scenarios modeled in the Adams-Laughlin study, the Earth’s long-term future is grim. During the next 3.5 billion years, our aging sun will increase in size and grow more than twice as bright as it is today. When this happens, “the Earth’s fragile biosphere will become seriously compromised,” Adams says.

The alternative to eventual incineration is being thrown out of the solar system into deep space. “The surface biosphere would rapidly shut down and oceans would freeze solid within one million years, but life could continue for some time near hydrothermal vents on the ocean floor, which are warmed by radioactive heat from deep within the Earth,” says Laughlin, a postdoctoral fellow at the University of California, Berkeley.

Adams and Laughlin’s detailed models for a frozen Earth have interesting implications for extra-terrestrial life. Adams maintains that liquid oceans could exist beneath thick ice sheets on many planets or moons of giant planets in the galaxy, especially planets that develop past the “snowline” in the planetary formation disk. “The snowline indicates the temperature where water ice can form in disk material,” Adams says. “The easiest places to get a large volume of water onto a rocky planet or moon are places where it’s cold enough to form ice.

“Since water is vital to the existence of life as we understand it, many people have suggested Jupiter’s moon, Europa, as a good candidate for supporting life,” Adams adds. “Our work suggests that the most likely places for extra-terrestrial life to develop would be in liquid oceans under ice. In other words, life on frozen icy bodies like Europa may be much more common in the galaxy than life on planets with liquid water on the surface like Earth. If true, this shift would greatly affect the possible branches of biological evolution in these extra-terrestrial environments.”

“Even though our solar system has never been disrupted by a passing star, these results imply that interactions between binaries and planets may be more common than has been believed,” Laughlin says. “It’s possible that millions of planetary systems throughout the galaxy have been affected by these binary scattering events, especially in the dense clusters where stars often form.”

Noting that many of the recently discovered planets in other solar systems have unusual elliptical orbits, Adams and Laughlin also have suggested that some of these orbits could be the result of a close encounter with a passing star or pair of stars.

The research project is supported by NASA and the University.