New Horizons reveals much, raises questions about Pluto

I overheard a little academic snark after a recent University of Washington astronomy colloquium. “It must be nice to be a planetary scientist,” said one attendee. “The answer to everything is, ‘I don’t know.’”

Will Grundy.
Photo: Lowell Observatory.

The topic of the day was Pluto, and the speaker was astronomer Will Grundy of Lowell Observatory. Grundy is a co-investigator for the New Horizons mission that flew past Pluto last July and will be beaming data back to Earth through the end of this year. He heads up the mission’s surface composition science theme team.

To be sure, Grundy’s talk was peppered with words like probably, puzzle, conjecture, speculation, and, yes, “We don’t know.” To be fair, we have learned quite a lot from a spectacular collection of snapshots beamed back to Earth from a dwarf planet three billion miles away. UW astronomy professor Don Brownlee talked about the scientific achievement, and the advances of the last 50 years, in his introduction of Grundy.

“Mariner 4 went to Mars and took 22 exciting pictures which we would now think were absolute dirt because they were 200 by 200 pixels and had very poor signal-to-noise ratio,” Brownlee said. “We’ve had this fantastic half-century of discovery of things where objects in the solar system went from dots to actual worlds. The last first-time is Pluto.”

One thing that we know fairly definitively is the variety of materials that are on Pluto’s surface. Grundy, who is a spectroscoper, showed many of the colorful images that reveal which compounds are there.

“The outer solar system would be a really colorful place if our eyes could just see a little farther out into the infrared,” Grundy noted, “but I guess it wasn’t advantageous to us running around on the African savannah to be able to distinguish methane ice from nitrogen ice.”

“The outer solar system would be a really colorful place
if our eyes could just see a little farther out into the
infrared,” says New Horizons scientist Will Grundy.
Mission scientists made this false color image of Pluto
using a technique called principal component analysis
to highlight the many subtle color differences between
Pluto’s distinct regions. Image: NASA/JHUAPL/SwRI.

Many other images showed the fascinating and varied terrain of Pluto, and this is where a lot of the we-don’t-knows come in. There are features that look for all the world like drainage canals, but it’s way too cold on Pluto for liquids. Perhaps the features were caused by glaciers, or some material we don’t know about. Other areas show what look like sand dunes with ripples on them, but Pluto’s atmosphere is too thin to blow sand around. Perhaps there was a thicker ancient atmosphere. Each photo revealed amazing detail and features, and many may well remain mysteries until more data can be collected.

“All of these different things are going on on different time scales,” Grundy said. “Sorting out the processes that we’re seeing here is going to be a fun challenge.”

The images are truly remarkable, though Grundy suggested they’re even better in higher resolution than he could display on the lecture-room screen. He suggested delving into the New Horizons image archive for some good viewing.

Pluto may seem insignificant to some, especially in light of its reclassification to dwarf planet, but Grundy said it’s well worth it to explore the “cold fringes of the solar system.”

“These things are really faint, really far away, really hard to get to, not huge,” he said. “Arguably they are the debris that’s left over from the formation of the giant planets, and they preserve a lot of clues about the planet-formation process specific to our solar system and perhaps general solar systems more broadly.”

“From my point of view, I’m just interested in exploration, just seeing what the objects out there are like.” Grundy continued. “If you like geology, or real estate, most of the solar system’s solid surface is out there.”

As New Horizons continues to beam back data it collected during last summer’s fly-by, it also is zipping toward another Kuiper Belt object, 2014 MU₆₉, at which it will arrive on New Year’s Day 2019.

There’s another chance to catch Grundy’s presentation about Pluto coming up this weekend. He is scheduled to give a talk titled “Pluto and Charon Up-close” at 2:15 p.m. Sunday, May 22 at the PACCAR IMAX Theater at the Pacific Science Center. It’s part of the center’s on-going observance of AstronoMay.