We previously examined how Neptune’s largest moon, Triton, could answer the longstanding question: Are we alone? With its nitrogen geysers discovered by NASA’s Voyager 2 spacecraft, possible interior ocean, and lack of craters, Triton could be geologically active, which makes it an excellent celestial body for future astrobiology missions. But Triton isn’t the only place on the edge of the solar system which garners interest for finding life beyond Earth, as one of the most familiar and well-known (former) planets also exhibits evidence of recent geological activity and crater-less surface features. This is everyone’s favorite dwarf planet, Pluto, which like Triton has only been visited by one spacecraft, this one being NASA’s New Horizons, in 2015. But even with only one visitation, we discovered so much about Pluto, and what it might be hiding, as well.
“Pluto’s huge nitrogen-ice-filled basin, Sputnik Planitia, is a dominant feature on the dwarf planet,” said Dr. Anne Verbiscer, who is a research professor in the Department of Astronomy at the University of Virginia, along with being the Deputy Project Scientist and a Co-Investigator on NASA’s New Horizons. “It’s the brightest (most reflective) area, with unique composition, and holds clues to the possible existence of a sub-surface ocean. And our current ‘recipe’ for life as we know it, includes liquid water. So, the possibility of liquid water beneath the surface of Pluto makes it intriguing for astrobiology and finding life beyond Earth.”
Color-enhanced image of Sputnik Planitia on Pluto taken by NASA’s New Horizons spacecraft in July 2015. (Credit: NASA / JHUAPL / SwRI)
As stated, NASA’s New Horizons is the only spacecraft to have visited and examined Pluto up-close, which happened on July 14, 2015, and discovered a far more complex world than previously hypothesized. It imaged atmospheric haze and surprisingly smooth surface features, to include Sputnik Planitia, which indicates recent, and potentially active, geologic activity. But how else has New Horizons helped improve our understanding of Pluto’s potential habitability?
“The importance of the New Horizons mission cannot be understated for the exploration of Pluto,” said Dr. Verbiscer. “We had a vague idea about the existence of Sputnik Planitia from Hubble Space Telescope (HST) visible images and its composition from ground-based near-infrared spectra. But nothing can compare to the views provided by New Horizons from its visible imaging camera (LORRI) and its near-infrared mapping spectrometer and color imager (LEISA/MVIC on the Ralph instrument).”
Several recent studies, to include a 2021 study in Nature, a 2021 study in JGR Planets, and a 2022 study in JGR Planets, have attempted to explain the forces behind Sputnik Planitia’s smooth appearance and crater-less terrain. A 2022 study in Icarus even hypothesized the possible existence of an interior ocean, as previously mentioned by Dr. Verbiscer.
“Pluto is a fascinating world that has captured the public’s interest since its discovery in 1930 through its up-close exploration by New Horizons in 2015,” said Dr. Verbiscer. “New Horizons confirmed that Pluto is a destination worthy of future exploration by orbiters and even landers. And until those future explorers arrive, continued observations of Pluto with improved instruments from both the ground and space (HST, JWST, etc.) will reveal more of Pluto’s secrets that will guide the planning of future exploration by spacecraft that will orbit Pluto and even land on its surface.”
Image of Pluto’s atmosphere taken by NASA’s New Horizons spacecraft in July 2015. (Credit: NASA / JHUAPL / SwRI)
What further secrets of Pluto will we unlock in the coming years and decades? Does it have an interior ocean and even harbor life as we know it, or as we don’t know it?
And with this, we wonder if Pluto will finally answer, “Are we alone?”