Sizing up rings
The dwarf planet Quaoar sports a ring that lies outside the orb’s Roche limit, an invisible line beyond which rings aren’t thought to be stable, Lisa Grossman reported in “This dwarf planet hosts an odd ring” (SN: 3/11/23, p. 11).
Reader Henry Leonard wondered if it’s possible the ring isn’t so unusual, that perhaps Quaoar simply has an unexpectedly large mass, resulting in a large Roche limit.
Astronomer Bruno Morgado of the Federal University of Rio de Janeiro is certain that the dwarf planet’s ring is an oddball. Morgado’s team used the orbital motion of Quaoar’s satellite, Weywot, to determine the dwarf planet’s mass. That revealed that the ring is way outside its Roche limit, Morgado says.
Down the drain
Fifty years ago, scientists discovered that Earth’s oceans slowly drain into the mantle. Today, it’s known that some water cycles back into the oceans, but just how much remains unclear, Erin Garcia de Jesús reported in “Oceans may be shrinking” (SN: 3/11/23, p. 4).
Reader Karen Schaffer wondered how this phenomenon influences sea level rise due to climate change.
The oceans are draining into Earth’s interior via plate tectonics at a much slower rate than they are rising due to modern climate change, says Clint Conrad, a geophysicist at the University of Oslo. About 280 million metric tons of ocean water leaks into the mantle every year, Conrad says. This seems like a lot, but it represents only a tiny fraction of a millimeter of sea level drop per year, he says. In comparison, Greenland and Antarctica together shed about 420 billion tons of ice into the oceans annually, which contributes an average of roughly a millimeter each year to global sea level rise (SN Online: 8/17/18).
At the current rate, the ice sheets will completely melt within about 50,000 years, Conrad says. But the slow and steady loss of ocean water to the mantle will continue for much of Earth’s lifetime….
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