We Don't Actually Know How Big Pluto Is

And nine other things we learned from New Horizon's AMA.

Feb 5 2015, 6:55pm

​Image:​ Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

The team at NASA's New Horizons mission—the first, long-awa​ited voyage to Pluto—took some time out of their busy, seven-days-a-​week work schedule to answ​er some questions on Reddit last night.

There were a lot of thoughtful, detailed, and sometimes quite technical questions from the redditors, which yielded some great new insight into the mission. Here are the top 10 most surprising things we learned from the AMA:

1. They don't actually know how big Pluto is

I mean, they have a pretty good idea, but Marc Buie, a member of the mission science team, revealed there are limits to the estimates they've been able to make so far. "The atmosphere makes it hard to measure the size directly," he wrote, adding the process isn't that complicated, we've just always been too far away. "It's almost as easy as printing a picture out and using a ruler. But we need to get the images from right at closest approach to get the best answer. In reality it will take some months to get a definitive result."

2. After Pluto, New Horizons is heading far, far away.

After the initial stop to get a close look at Pluto, the New Horizons team will propose extending the mission to investigate a Kuiper Belt Object (they've got it narrowed down to two). But it won't stop there. Principal investigator Alan Stern wrote that NH is on an "escape trajectory" from the solar system and could potentially be sending us remote data for decades.

3. When it launched, New Horizons was the fastest spacecraft ever sent into Space. 

But it's not the fastest in space now. Since the Voyager crafts had more gravity assists, they are now moving much faster (and are much further out, at more than 12 billio​n miles from Earth) than New Horizons.

The New Horizons team poses for the AMA proof photo. Image: ​Reddit

4. In the future, we'll communicate with spacecrafts using lasers. 

One of the issues with having a spacecraft so far from Earth is that it takes a long time for data to travel back to us. The current download speed is about 1 kilobyte per second, and the team estimates it will take more than a year after the mission to get all the data collected. In the future they will use lasers instead of X-beams, making this process much faster. NASA has already tested using lasers to communicate with Earth f​rom the moon

Michael Vincent, the payload systems engineer wrote: "[It's] not easy at all [to aim the laser] and we don't have laser comm on New Horizons. The first demonstration was Earth-to-moon, and that was successful. The next step is Mars."

5. New Horizons could discover that Pluto has more moons. 

They'll be able to detect moons as early as June and there's a chance there are more than the five known moons. "There could be lots, particularly far from Pluto. In close, the system is gravitationally jammed packed, so we expect at most only a few," wrote Stern. "But then again, this is first time exploration, so we could be really surprised!"

6. NASA gets to name any geological discoveries, but it won't be after themselves. 

Any major geological objects on the dwarf planet will be named by the New Horizons team. They said they have a list going, but usually only name something after a person posthumously. Given their affection for Pluto's discoverer Clyde Tombaugh (his family has celebrated with the team at major milestones, they relea​sed the first images on his birthday, and his freak​ing ashes are on board the ship) don't be surprised if there's a Tombaugh Mountain in Pluto's future.

7. Pluto is actually red, brown, and black. 

We already kind of knew this from the Hubble maps, but those were mostly estimations. As New Horizons approaches the dwarf planet, we'll have our first close-up color photos to show us exactly what the surface looks like. Charon, Pluto's biggest moon, will just be grey though, the team said.

The best images we have of Pluto so far, via Hubble. Image: NASA, ESA, and M. Buie (Southwest Research Institute)

8. There's a good reason why New Horizon is not orbiting Pluto.

A lot of people were curious why they're just doing a pass by instead of orbiting the dwarf planet for a good long look. Deputy project scientist Leslie Young explained: "New Horizons is traveling at about 14 km per second. New Horizons launched on a huge Atlas V rocket to get to that speed. To slow down, we'd need the fuel of another Atlas V! But to carry that, we'd need more fuel, and then more fuel to carry that fuel." You can see the problem.

9. If aliens find it, they might be very confused. 

While Voyager famously included​ a golden record with greetings, pictograms, music, and sounds from Earth in case aliens find it, New Horizons does not. It does have a CD filled with the names of individuals who requested to have their name flown to Pluto, as well as Tombaugh's a​shes, so any curious alien lifeforms might have a harder time deciphering what this thing is for.

10. The team has varied opinions on breakfast food:

Maybe not that surprising, actually.