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A strange spot emerged on Venus last week, and astronomers are not sure what caused it. They hope future observations will reveal whether volcanic activity, turbulence in the planet's atmosphere, or charged particles from the sun are to blame.
Amateur astronomer Frank Melillo of Holtsville, New York, first spotted the new feature, which is brighter than its surroundings at ultraviolet wavelengths, on the planet's southern hemisphere on 19 July. That same day, an amateur observer in Australia found a dark spot on Jupiter that had been caused by a meteoroid impact.
The Venus spot was confirmed by other observers, and images from Europe's Venus Express, the only spacecraft in orbit around the planet, later revealed that the spot had appeared at least four days before Melillo saw it.
Observations show that the spot had already spread out somewhat by the end of last week, and astronomers are awaiting more recent observations from Venus Express.
The spot is bright at ultraviolet wavelengths, which may argue against a meteoroid impact as a cause. That's because rocky bodies, with the exception of objects very rich in water ice, should cause an impact site to darken at ultraviolet wavelengths as it fills with debris that absorbs such light, says Sanjay Limaye of the University of Wisconsin-Madison and a member of the Venus Express team.
Another possibility is that a gust of charged particles from the sun could have created the glow by energising a patch of the upper atmosphere. Alternatively, waves in the atmosphere, which trigger turbulence and are thought to carry material up and down, could have concentrated bright material to create the spot.
A volcanic eruption is another suspect. Venus boasts the most volcanoes of any planet in the solar system, and nearly 90% of its surface is covered by basaltic lava flows, although no 'smoking gun' has yet been found for current volcanic activity. But an eruption would have had to be very powerful to punch through a dense layer in Venus's atmosphere to create the spot some 65 to 70 kilometres above the planet's surface.
"It's fair to say something unusual happened on Venus. Unfortunately, we don't know what happened," Limaye told New Scientist.
Something has smashed into Jupiter, leaving behind a black spot in the planet's atmosphere, scientists confirmed on Monday.
This is only the second time such an impact has been observed. The first was almost exactly 15 years ago, when more than 20 fragments of comet Shoemaker-Levy 9 collided with the gas giant.
"This has all the hallmarks of an impact event, very similar to Shoemaker-Levy 9," said Leigh Fletcher, an astronomer at NASA's Jet Propulsion Lab in Pasadena, California. "We're all extremely excited."
The impact was discovered by amateur astronomer Anthony Wesley in Murrumbateman, Australia at about 1330 GMT on Sunday. Wesley noticed a black spot in Jupiter's south polar region (see image) – but he very nearly stopped observing before he saw it.
"By 1am I was ready to quit ... then changed my mind and decided to carry on for another half hour or so," he wrote in his observation report. Initially he suspected he was seeing one of Jupiter's moons or a moon's shadow on the planet, but the location, size and speed of the spot ruled out that possibility.
'Stroke of luck'
After checking images taken two nights earlier and not seeing the spot, he realised he had found something new and began emailing others.
Among the people he contacted were Fletcher and Glenn Orton, also at JPL. They had serendipitously scheduled observing time on NASA's InfraRed Telescope Facility in Hawaii for that night.
"It was a fantastic stroke of luck," Orton told New Scientist.
Their team began observations at about 1000 GMT on 20 July, and after six hours of observing confirmed that the spot was an impact and not a weather event.
"It's completely unlike any of the weather phenomena that we observe on Jupiter," Orton says.
The first clue was a near-infrared image of the upper atmosphere above the impact site. An impact would make a splash like a stone thrown into a pool, scattering material in the atmosphere upwards. This material would then reflect sunlight, appearing as a bright spot at near-infrared wavelengths.
To orbit Neptune and Uranus That would be wonderful..
Unfortunately, whatever funds NASA has left after the government goes on its inevitable "austerity program" will probably go to the next Mars mission.
The estimated cost for the full mission would place it in at the lower end of the larger flagship range (~$2B FY15 dollars). The mission could be descoped to the cost of a small flagship missions (~$1.5B) by addressing Tier 1 objectives only.