The New Horizons spacecraft has nearly finished its 16-month dispatches from Pluto, Nasa scientists said on Tuesday, as they unveiled new hints of clouds and the craft’s next destination in the distant ring of the solar system, reports The Guardian.
Researchers had found last year that Pluto has layers of strange hazes towering half a million feet (200km) in the sky, but saw none of the swirling storms that cover gas giants or the wisps of condensation that gather in Mars’ thin atmosphere. On Tuesday, at the annual meeting of the American Astronomical Society’s planetary scientists, principal researcher Alan Stern presented new evidence that clouds may form at dusk and dawn on Pluto.
Nasa had found seven candidates for clouds, Stern said, each “quite suggestive of possible but rare condensation clouds on Pluto”. He cautioned, however, that “none of them can be confirmed as clouds because all of them are very low lying, close to the surface” – and outside the reach of New Horizons’ instruments.
The cloud candidates were not decked or layered like those on Earth, he added, but rather suggest a sky “like it is in the western United States”. That sky would be “99 per cent free of clouds”, he said, but it would suggest “weather on Pluto is even more complex than we imagined.”
Clouds have a specific definition, he added: “discrete features that are optically thick and therefore would block the surface below them”. Stern said that, if confirmed, the clouds might be like a fog made of uncommon gases, like ethane, acetylene or possibly methane, that condense at dawn and dusk of Pluto’s long days – each one lasts 6.4 days on Earth.
“The first flyby has given us a fantastic taste of a very dynamic and changing environment, but it’s not enough,” Stern said. “In order to confirm we would have to go back with more instrumentation and more time.”
New Horizons is already well past Pluto and on its way toward a new destination, itself a billion miles beyond the dwarf planet. Stern said Nasa was only in the earliest stages of talks for a follow-up mission to Pluto, and that any mission would take time. “Although New Horizons was the fastest spacecraft ever launched, it still took it nine and a half years.”
The spacecraft already has sent an enormous amount of data back to scientists, who will finish the download from Pluto’s flyby on Sunday, nearly a year and a half after New Horizons became the first manmade object ever to visit the dwarf planet. Analysis of some of that data, Nasa scientist Bonnie Buratti told reporters on Tuesday, showed Pluto’s giant, heart-shaped region is one of the most reflective places in the solar system.
Pluto’s icy surface varies in its brightness, from nearly 100 per cent at the heart to only eight per cent in other regions. Buratti said that intense brightness, like “freshly fallen snow”, suggests intense activity akin to that on Enceladus, the frozen moon of Saturn where scientists have seen plumes erupting from a saltwater ocean beneath the ice.
The body that Pluto looks like, it turns out, is Iapetus, a “strange, very weird moon of Saturn,” Buratti said, calling the moon “this world where half is very dark, sweeping up dark particles from the Phoebe ring [the largest ring of Saturn], and the other half is bright, not as bright as Pluto.”
She said these clues suggest similar activity on Eris, another dwarf planet in the Kuiper belt, the distant ring of the solar system where Pluto orbits.
New Horizons is now on its way to MU69, another object in the belt, and scheduled to come within 3,000km of it around New Years Day 2019. Researcher Amanda Zangari said that MU69 could provide a look at “one of the ancient building blocks of the planets”, since the belt contains the “primordial remnants of the disc that formed the planets” about four billion years ago.
Stern refused to speculate on what New Horizons would find there. “We’ve never been to something like MU69,” he said. “I don’t make predictions because they’re so often wrong.”