There are tropics on Pluto. While this may sound counterintuitive, its climate means that there are “warmer” parts of the world relative to its colder, arctic regions. As new research presented at the 2016 Lunar and Planetary Science Conference this week reveals, this diverse climate means that rivers and lakes of liquid nitrogen are likely to form at the surface.

Even with less than half of New Horizon’s data, scientists are unravelling more and more secrets about the dwarf planet by the day. The latest comes by way of researchers at NASA who confirm that Pluto – despite being on average 5.9 billion kilometers (3.7 billion miles) away from the Sun – has seasons.

The central tropical region of Pluto, from 60° north to 60° south, experiences the Sun passing directly overhead. Its arctic region above 30° north experiences prolonged sunlight in the summer months, whilst the arctic region beneath 30° south is utterly frigid in a simultaneous winter.

Pluto is tipped over on its rotational axis at 120°, rather wonky compared to Earth’s 23° tilt. As a result of this, during a northern arctic summer, the region receiving the most heat is its north pole.

^{Go home Pluto, you’re drunk: The extreme axial tilt of the dwarf planet. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute}

The dwarf planet wobbles and shakes on its axis as it orbits the Sun just like Earth does, meaning that these arctic regions advance and retreat over cycles of hundreds of thousands of years. One region, however, never experiences arctic climates.

This band, between 13° N and 13° S, appears to have been gouged out, in that there’s a dark, deep stripe compared to the rest of the planet. The researchers think that the constant “warm” band here means that ice and volatiles – compounds that evaporate at low temperatures – couldn’t accumulate here under the Sun’s constant bombardment.

^{The dark equatorial band. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute}

Incidentally, the icy world’s elliptical orbit means that it moves between 50 Earth-Sun distances at its furthest point from the Sun and 30 Earth-Sun distances at its nearest point. Consequently, the temperature difference between a distant summer and a closer summer are more extreme than almost anywhere else.

This is all still relative, mind you: a summertime peak temperature is still around -200°C (-330°F). As Pluto takes 248 Earth years to rotate around the Sun, these summers and winters last for more than a century.

A second paper presented at the conference reveals that Pluto’s atmospheric pressure has varied wildly over its history, driven by these long-term orbital and rotational changes. It has ranged from about one-ten-thousandth right up to up to one-fifth of Earth’s.

These enormous changes in atmospheric pressure would have a distinct effect on the surface of the world; at higher pressures, the abundant nitrogen at the surface would remain a liquid instead of a gas. This means rivers, floods and lakes of liquid nitrogen may haved existed on Pluto.

Researchers noted that these features would be relatively common around 800,000 years ago, when temperatures were hot enough to lead to widespread melting. There may be some still around today near the equatorial region, although they have yet to be spotted. Frozen lakes, however, have been seen, and these ice reservoirs were almost certainly once liquid.

^{An enhanced color image of Pluto highlighting its wildly varying geological features. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute}

Pluto is the gift that just keeps on giving, it seems. A plethora of papers have recently revealed that Pluto’s atmosphere isn’t disintegrating as much as we previously thought, and most significantly, the surface is “active” – essentially meaning that mountain building and perhaps cryovolcanism is still happening on this distant, icy sphere.

 

 

^{Above is a video of the research presented from the LPSC.}