Freeze or fry: physicist predicts solar system’s ultimate fate

February 15, 2000

WASHINGTON, D.C.—While most scientists want to know how our solar system began, Fred Adams is more interested in how it will end. His prognosis is grim. In the short term, we either freeze or fry. In the long term, we decay.

Adams presented his vision of the solar system’s fate in a presentation at the annual meeting of the American Association for the Advancement of Science held here Feb. 17-22.

During the next 7 billion years, our aging sun will gradually exhaust its fuel supply and collapse into a white dwarf, says Adams, an associate professor of physics at the University of Michigan. The sun will mushroom in size before it collapses and shine so brightly that it will incinerate the Earth and the inner planets in the solar system. But as soon as 3.5 billion years from now—long before the planets go up in smoke—all life in the Earth’s fragile biosphere already will have perished from the heat.

There is one escape clause in this fiery scenario, according to Adams. We may be rescued by a close encounter between our solar system and a passing star. Adams and Gregory Laughlin, a scientist at NASA‘s Ames Research Center, used a computer and statistical processing calculations to model possible interactions between nearby binary stars and the orbits of the Earth, sun and outer planets, especially Jupiter.

“Jupiter is vulnerable to gravitational interactions with a passing star,” Adams explains. “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.”

Should the Earth be thrown out of the solar system into deep space, its oceans would not freeze solid for about 1 million years, according to Adams. “Life could continue to thrive near hydrothermal vents on the ocean floor, which are warmed by radioactive heat from deep within the Earth,” he says. In fact, Adams maintains that the most likely place to find extra-terrestrial life may be in liquid oceans beneath thick ice sheets on planets or moons of giant planets, such as Jupiter’s moon, Europa.

In the far, far distant future—long after our solar system has met its ultimate fate—the galaxy will move into what Adams calls the Degenerate Era. “The only stellar objects remaining will be white dwarfs, brown dwarfs, neutron stars and black holes,” he says. During this era, galaxies will begin to relax dynamically with some remnants of stars moving out to the edge of the galaxy and others falling to the center. Invisible dark matter gradually will be captured and converted into energy to keep the few remaining white dwarf stars shining weakly for a little while longer.

“Eventually the supply of dark matter particles will be exhausted,” Adams says. “Then the mass of white dwarfs and neutron stars will begin to dissipate through a process called proton decay. A white dwarf fueled by proton decay would generate approximately 400 watts or enough to run a few light bulbs.”

Even black holes won’t last forever. Fed by material falling to the galaxy’s center, black holes will grow larger for a long time. But even their enormous mass must eventually dissipate into thermal radiation, photons and other decay products.

Once the black holes have radiated away, Adams says all that remains will be a diffuse sea of electrons, positrons, neutrinos and radiation suspended in nearly complete and total blackness.

This U-M research study was supported by the National Science Foundation, NASA and the U-M Department of Physics.

Fred AdamsAmerican Association for the Advancement of SciencephysicsNASANational Science Foundation