The Sun Will Eventually Engulf Earth--Maybe
Researchers debate whether Earth will be swallowed by the sun as it expands into a red giant billions of years from now
By David Appell
The future looks bright—maybe too bright. The sun is slowly expanding and brightening, and over the next few billion years it will eventually desiccate Earth, leaving it hot, brown and uninhabitable. About 7.6 billion years from now, the sun will reach its maximum size as a red giant: its surface will extend beyond Earth’s orbit today by 20 percent and will shine 3,000 times brighter. In its final stage, the sun will collapse into a white dwarf.
Although scientists agree on the sun’s future, they disagree about what will happen to Earth. Since 1924, when British mathematician James Jeans first considered Earth’s fate during the sun’s red giant phase, a bevy of scientists have reached oscillating conclusions. In some scenarios, our planet escapes vaporization; in the latest analyses, however, it does not.
The answer is not straightforward, because although the sun will expand beyond Earth’s orbit, or one astronomical unit (AU), it will lose mass along the way. As a result, Earth should drift outward as the gravitational tug lessens over time. (At its maximum radius of 1.2 AU, the sun will have lost about one third of its mass, compared with its current heft.) In this way, Earth could escape solar envelopment.
But other factors complicate the analysis. Drag on the planet from the sun’s outermost, tenuous layers will cause Earth to drift inward. Smaller forces from the other planets—all in turn reacting to the same reducing, expanding sun—are even more difficult to account for completely.
Earlier this year two teams reported different kinds of
calculations indicating that Earth will be swallowed up by the sun. In a
calculation that would thrill any college junior studying classical mechanics,
Lorenzo Iorio of
Iorio’s paper, submitted to Astrophysics and Space Science, has not yet been peer-reviewed. Several scientists question whether quantities that Iorio assumes are small will indeed remain small throughout the sun’s evolution.
Even if Iorio got his number crunching wrong, he may have
the right answer. In an analysis published in the May Monthly Notices of the
Royal Astronomical Society, Klaus-Peter Schröder of the
Could Earth be saved if someone is still left at home? In a
bold piece of astronomical engineering, Don Korycansky of the
Note: This article was originally printed with the title, "A Solar Big Gulp".
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