With New Horizons now 63 AU out, it’s time to ponder that record hibernation period that the spacecraft just went through. Over 10 months long, this one had the same goal as previous such periods, to hold down operating costs but also give a break to onboard instrumentation in hopes of augmenting mission lifetime. As a kid, I often thought how cool it would be to be involved with a distant spacecraft. For some reason I always visualized this as being here on Earth while working with a craft beyond the Solar System. So maybe I was dreaming more of being a flight controller than an astronaut.

I hadn’t realized until reading Alan Stern’s recent update that while hibernation means there are no commands and responses going back and forth, the craft does continue active data gathering from its Solar Wind at Pluto (SWAP) plasma detector and the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument. The Student Dust Counter is also in operation. Since awaking early in the summer, New Horizons has been delivering data from these instruments back to Earth.

I see that future flybys of Kuiper belt objects (KBOs) are still a distinct possibility, assuming that one can be found within range of the vehicle. And yes, the Vera Rubin Observatory is already in use in the search for such objects, with planning extended to requests for time on the Roman Space Telescope, now scheduled for launch within days. Writing about New Horizons always comes with a tinge of melancholy as I contemplate the fact that no successor is ready, but it’s a relief to see how active this tough little craft continues to be. There are good successor concepts out there, but none are currently funded.

Meanwhile, we have the interesting news about possible liquid flows on Pluto’s surface, revealed by New Horizons images of Sputnik Planitia, the nitrogen glacier whose northern regions reveal convection cells separated by features that suggest liquid nitrogen has flowed there in the past. The new work out of Southwest Research Institute (SwRI) and published in the Planetary Science Journal, suggests that this process continues, doubtless through liquid nitrogen upwelling from beneath the glacier.

SwRI’s Kelsi Singer, one of the study’s co-authors, comments:

“The surface of Sputnik Planitia is quite young, probably less than one million years based on modeling of the surface overturn, and thus these features that we are looking at must have formed since then. Pluto has many unique terrains seen nowhere else in the solar system, and this area of Sputnik Planitia is one of them. Its surface provides a different set of conditions compared to what we are used to on Earth, and exploring that allows us to better understand how materials behave in environments that are difficult to produce on Earth.”

Image: Pluto’s northern Sputnik Planitia glacier (in the western or left side of Pluto’s bright heart) is shown here in a color mosaic made from NASA’s New Horizons imagery. The direction of north is shown on the image. The image is ~ 700 x 350 kilometers across. The red box has been added to show most of the region containing dark features attributed to the wetting of the glacier by liquid nitrogen sourced from a “basal melting” process beneath the glacier. NASA/Johns Hopkins APL/SwRI.

These findings are based on studies of a glacial surface far from Earth and involve liquid nitrogen rather than water, but it’s interesting that the paper reports that the surface patterns on this region of Sputnik Planitia have darkened in ways that are similar to Earth glaciers that have undergone their own wetting by subsurface liquid. The team worked with images from the Landsat 9 satellite that included the Greenland ice sheet. Computer models of glacial melting led by Orkan Umurhan (SETI Institute) reveal a transport mechanism to the surface and indicate an icy flow that can persist on the surface for short periods, which would account for the dark features.

And there is another Earth analogue that perhaps comes into play. From the paper:

We have posited that the striking, dark, irregular linear and diffuse features prevalent at the northern margin of SP are manifestations of the upwelling of liquids or liquid slurries from beneath the SP ice sheet. We have further posited that these liquids were created as a basal melt at depth below the glacier, and we have quantitatively shown the plausibility that such a mechanism can then advect through conduits to the surface of SP where it will horizontally spread out, leaving a darkened surface akin to that observed in northern SP. The buoyant ascent of liquid nitrogen through the denser N2 ice is akin to terrestrial volcanism where less dense basaltic melt rises through cold continental crust.

Does this process occur on other dwarf planets in the Kuiper Belt? We won’t know that until we have mapping missions to objects like Eris. The paper also mentions the obvious candidate at Neptune, the large moon Triton, as a possible example of such processes factoring into the geysers Voyager 2 observed during its flyby. For that matter, it’s fascinating to consider that despite the success of New Horizons at Pluto/Charon, over half the planet (I know I’ll get emails about calling it that) remains unmapped at high resolution because of the geometry of the encounter. So for the time being, we don’t even know whether apparent flows like that at Sputnik Planitia occur elsewhere.

The SETI Institute’s Umurhan points out that the physics of solid nitrogen materials under stress and strain are not well understood, and have to this point “never been studied in real detail in the laboratory.” We need, in other words, to go out there and look, and New Horizons has just reminded us why.

The paper is Stern et al., “Evidence for Possible N2 Basal Flow beneath Pluto’s Northern Sputnik Planitia,” Planetary Science Journal Vol. 7, No. 7 (31 July 2026), 185 (full text).