A sudden
bright spot that appeared in the clouds of Venus just days after a comet left a
bruise on Jupiter has scientists stumped as to its cause.
Venus'
bright spot, first noticed by amateur astronomer Frank Melillo of Holtsville, NY
on July 19, is not the first such brightening noticed on our cloudy neighbor,
said planetary scientist Sanjay Limaye of the University of Wisconsin-Madison.
"We
have seen such events before," he told SPACE.com.
This time
is a little different though because the brightening is confined to a smaller
region, Limaye said. It also came in the wake of Jupiter's own
new (dark) spot, believed to be the result of a comet impact — Limaye
attributes the fortunate confluence of the two events for the attention Venus
is now getting in the astronomical community.
After
Melillo reported the spot, other amateur astronomers and the European Space
Agency's (ESA) Venus
Express spacecraft confirmed the presence of the blemish.
The new
Venus Express images show that the bright spot actually appeared in the
planet's southern hemisphere four days before Melillo saw it and that it has
since begun to spread out, becoming stretched by the wind's in Venus' thick
atmosphere.
But just
what caused the brightening is still a mystery. Theories have abounded, from a
volcanic eruption
to solar particles interacting with the planet's atmosphere.
Limaye says
the volcano explanation is unlikely, for several reasons: Volcanoes on Venus
seem to be less likely to blow their tops in Mount St. Helens-type fashion,
instead behaving more like the oozing lava factories of Hawaii, so their
eruptions wouldn't likely produce huge clouds of ash and steam. Also, it is
unlikely that the explosions would have the power to push through to the other
layers of Venus' extremely dense atmosphere.
Limaye
doesn't completely rule out the possibility, however. "It's possible, we
just don't know," he said.
Another
explanation is that a coronal mass ejection (an energetic plume of plasma from
the sun's corona) or the solar wind could have interacted with the clouds of
Venus.
These
"could cause something, we don't know what," Limaye said.
Yet another
possibility is some internal change in Venus' atmosphere that could alter cloud
particles and make them more reflective (and therefore brighter as viewed from
space).
"Clearly
something in the cloud properties changed," Limaye said.
Even though
these events have been seen previously, most notably in Jan. 2007, our limited
knowledge about the workings of Venus' atmosphere and lack of enough spacecraft
to comprehensively study the planet hasn't narrowed down the list of possible
causes, Limaye said.
"Right
now, I think it's anybody's guess," he said.
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