A cloud in Pluto’s twilight zone?

Remember this image of Pluto, backlit? Careful analysis of it may have revealed the only cloud found so far in this world’s atmosphere.

Pluto, backlit. The edge of light around the planet is what scientist's call it's twilight zone. Image via NASA/ Johns Hopkins/ SWRI.

Pluto, backlit, approximately 13,400 miles (21,550 km) from the dwarf planet, 19 minutes after New Horizons’ closest approach. The rim of light is what scientist’s call its twilight zone. Image via NASA/ Johns Hopkins/ SWRI.

NASA said on June 2, 2016 that images from the New Horizons spacecraft – which passed Pluto last July – might have revealed a cloud in Pluto’s sky. The famous image above shows what astronomers call Pluto’s twilight zone, a never-before-seen view of the planet, with the sun on the other side of Pluto. NASA said:

Looking back at Pluto with images like this gives New Horizons scientists information about Pluto’s hazes and surface properties that they can’t get from images taken on approach.

The below shows a detail of Pluto’s twilight zone, including what NASA called:

… an intriguing bright wisp (near the center) measuring tens of miles across that may be a discreet, low-lying cloud in Pluto’s atmosphere; if so, it would be the only one yet identified in New Horizons imagery.

NASA also explained:

This cloud – if that’s what it is – is visible for the same reason the haze layers are so bright: illumination from the sunlight grazing Pluto’s surface at a low angle. Atmospheric models suggest that methane clouds can occasionally form in Pluto’s atmosphere.

The scene in this inset is 140 miles (230 km) across.

Read more from New Horizons

Why did it take the New Horizons team so long to discover this cloud? In fact, New Horizons is still sending back data from Pluto and will continue to do so for some months to come. As for the data, scientists will likely be pouring over these bits of information and making new discoveries – revealing Pluto’s secrets – for decades.

After all, the New Horizons mission to Pluto took lead investigator Alan Stern a lifetime to accomplish. For some of us, it’ll be the only Pluto mission in our entire lives.

Bottom line: Data analysis from New Horizons’ July 14, 2015 sweep past distant Pluto may have revealed a cloud in a famous image of Pluto’s twilight zone.

Deborah Byrd