Bonus Factismal – Colder Than Hades

In the next 24 hours, we will visit the last of the “classical planets”; the NASA New Horizons probe will finally arrive at Pluto. That’s a pretty big deal and it is very special in all sorts of ways.

New Horizons' position as of July 13 (Image courtesy NASA)

New Horizons’ position as of July 13
(Image courtesy NASA)

Why is this so important?
This visit is important for two main reasons. First, this is our “last first”; this is the last time that we will visit a “classical planet” for the first time. By doing so, we will finish a plan that was first dreamed up in the 1970s. Known as the Grand Tour, the idea was to visit every planet in the Solar System. NASA wanted to launch four probes that would use gravitational slingshots where the probe swings “behind” a planet and steals some of the planet’s momentum; by doing so, the probes could visit every planet in the Solar System. That was the good news. The bad news was that because the probes would be speeding by, all that they could do is take a few quick pictures before heading off to their next destination. They’d be like tourists hanging out of a train, taking snapshots as they whizzed past the various cities of Europe – which is why they called it a Grand Tour.


The “semi-Grand Tour of the Voyager probes
(Image courtesy NASA)

When budget considerations cut the Grand Tour from four probes to the two Voyagers, Pluto dropped off the list of targets. So Voyager 1 visited Jupiter and Saturn in 1980, and Voyager 2 visited Jupiter (in 1979), Saturn (in 1981), Uranus (in 1985), and Neptune (in 1989), but no probe visited Pluto. Until now.

The Pluto system (Image courtesy NASA)

Our best image of Pluto, two years ago
(Image courtesy NASA)

Our best image of Pluto two days ago (Image courtesy NASA)

Our best image of Pluto two days ago
(Image courtesy NASA)

The other reason that a visit to Pluto is important is all of the things that we’ve learned about the planet since the Grand Tour was first proposed. Back in 1970, we thought that Pluto was a big, rocky planet somewhere between the size of Mercury and the Moon. Back then, we divided the planets up into big, low density gas giants (like Jupiter and Saturn) and small, high density rocky planets (like Earth and Mars). We didn’t know then that Pluto had any moons, nor that it was only one out of hundreds of similar planets in the outer Solar System. Today, we know that Pluto is very small but also very low density; it has more in common with Jupiter’s moon Europa than with our Moon. By taking a lot of measurements of Pluto, we hope to learn more about how these small icy bodies form – and what that means for life in the Solar System.

A plot of planetary size versus density. Notice how Pluto ends up with the junk.

A plot of planetary size versus density. Notice how Pluto ends up with the junk.

Excuse me; did you say life?
That’s right. Our current best model for Pluto is that it is a large, icy ball. If it is like Europa, Titan, and Enceladus, then it is probably divided into three main parts: a thick crust of ice, a small core of solid rock, and a thick mantle of water between the two. If there is enough heat from tidal friction and from radioactivity, then that mantle may be liquid water. And, since life started in the oceans on Earth, there may be life in those deep, dark oceans on Pluto.

The inside view of Pluto; that frozen water may actually be liquid  (Image courtesy NASA)

The inside view of Pluto; that frozen water may actually be liquid
(Image courtesy NASA)

There are some other evidences for the possibility of life on (or rather in) Pluto. As is the case for most things out in the Kuiper Belt, we have seen plenty of evidence for organic molecules ranging from methane (found almost everywhere in the Solar System) to tholins (found on most icy bodies in the Outer Solar System). These molecules could provide the starting point for life.

Something so important means that we’ll spend a lot of time there, right
Remember that “Grand Tour” with the tourists hanging out the windows? Yeah, that is what will happen here. At 6:49 AM CDT on Tuesday, July 14, New Horizons will be getting closer and closer to Pluto. At 6:51 AM CDT, New Horizons will be getting farther and farther away. For that brief moment, the probe will be as close as it ever will be to Pluto, a mere 7,800 miles away from the surface. But that doesn’t mean that the science will stop.

A plot of what we know is in orbits similar to Pluto's (Image courtesy CEPS)

A plot of what we know is in orbits similar to Pluto’s
(Image courtesy CEPS)

We’ve been taking increasingly better pictures of Pluto for the past two weeks. And we’ll take even better images as we get closer over the next day. Then we’ll take pictures that are a little worse, then ones that are not-so-good. And then we’ll turn New Horizons’ metaphorical eyes towards its next target, PT1 out in the depths of the Kuiper Belt.

The whosey-whatsis?
The Kuiper Belt is a set of small, left over bits of junk from when the Solar System first formed. Like the asteroid belt, it is mostly empty space with the occasional chunk of rock. Unlike the asteroid belt, these rocks are mostly fresh from the freezer and still have much of the original stuff that the Solar System was made from. Some planetologists think that Pluto is a Kuiper Belt Object that was almost captured by Neptune. New Horizons should make the trip from Pluto (at 32.9 AU) to PT1 (at 43.4 AU) in just under four years and arrive in January of 2019. Right now, we have two probes in the Kuiper Belt (Pioneer 10 and 11) and two probes that have passed through it and are approaching the edge of the Solar System (Voyager 1 and 2). But New Horizons will be the first probe to visit the belt with all of its instruments still working.

So how do I get to see the good stuff?
That’s easy. NASA is making the images available to the public just as soon as they finish downloading. So at about 7 PM CDT on Tuesday, July 14, the first of the close-up data will be received by NASA. About 7 AM the next day, the pictures should be available on the web at the New Horizons web site:

But you said that the probe would be at Pluto at 6 AM. What gives?
Don’t forget the time it takes the radio signal to get from Pluto to Earth. That’s about four and a half hours. (Fun geek point: the distance that light travels in an hour is sometimes referred to as a “light hour”. So Pluto is about four and a half light hours away right now.) And then there is the time it takes to process the image, both at Pluto and then again here on Earth. So even though they take the pictures at 7 AM, it will take until 7 PM for the pictures to travel the distance from Pluto to here and be processed.

2 thoughts on “Bonus Factismal – Colder Than Hades

  1. Is part of the 12 hours maybe processing or transmission time? I saw 4.5 hours as the speed of light delay in an article on last week’s “glitch” and that is close to what I get with a back-of-an-envelope estimate.

    • That’s a nice catch; thank you. Yes, the actual “flight time” for the data is only about 4.5 hours. Then there is the processing time on New Horizons’ end to store and compress the data plus the transmission time (they are using the interplanetary equivalent of dial-up while we’ve moved on to broadband), reception time here, and then the time it will take to decrypt and process the data before putting it on the web for all to see.

      And thank you for commenting on my blog! It is always good to meet another lover of all things science.

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