1532: New Horizons

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New Horizons
Last-minute course change: Let's see if we can hit Steve's house.
Title text: Last-minute course change: Let's see if we can hit Steve's house.


New Horizons is a NASA mission launched in 2006 to study the dwarf planet Pluto and its moons. Its closest approach to Pluto was on July 14, 2015 (NASA countdown clock), two weeks after the publication of this comic. In April and May 2015, it captured the first images of Pluto with enough resolution to see some details on Pluto's surface (NASA photos from 12 April to 12 May). These images are similar to the second pane of the comic, with Pluto shown as a gray dot only a few pixels wide. Dawn is a NASA mission launched in September 2007 to study the asteroid Vesta and dwarf planet Ceres. Its closest approach to Vesta began on July 16, 2011 by the Vesta approach, and entered orbit around Ceres on 6 March 2015. And in fact the pictures of Ceres are still in a much better resolution like in this comic 1476: Ceres, but these images are also still mysterious.

On the day this comic was published, New Horizons was at 0.34 AU from Pluto and 32.55 AU from the Sun (Johns Hopkins University's New Horizons page). One Astronomical unit (AU) is the approximate distance of Earth from the Sun, or about 150 million kilometers.

Distances from the Sun by semi-major axis: Vesta 2.36 AU; Ceres 2.77 AU; Jupiter 5.20 AU; Pluto 39.26 AU.

A slingshot maneuver is a technique where a spacecraft is maneuvered or accelerated with the help of a gravitational field. In the comic, presumably someone named Steve made the calculations for the New Horizons spacecraft to accelerate toward Pluto using Jupiter's gravity.

In the first panel we see Cueball and Ponytail standing in front of a computer monitor and observing a series of images sent back from New Horizons as it approaches the planet. They are about to see the dwarf planet Pluto with the highest resolution ever.

As the spacecraft gets closer, the images return... Earth. Steve had miscalculated the gravity assist and the spacecraft was about to crash into Earth.

Because the spacecraft carries 10.9 kg (24 lb) of radioactive plutonium-238, a crash on earth is extremely dangerous. It was estimated that a worst-case scenario of total dispersal of on-board plutonium during the launch would spread the equivalent radiation of 80% the average annual dosage in North America from background radiation over an area with a radius of 105 km (65 miles) (Draft Environmental Impact Statement for the New Horizons Mission). Because of decay during the flight, the situation would be slightly less dire if it crashed years later, but still a major disaster.

Less importantly, this is a huge embarrassment, especially in front of the successful Dawn team, who were the first to get a probe to visit a dwarf planet. Part of the joke is the utter implausibility of such an error being made, and then not being detected.

The title text suggests the team is considering crashing the probe into Steve's house as punishment for his errors. However, doing so would expose Steve's neighbors to potentially lethal levels of radiation. Therefore, the team would most likely have to crash the probe into an unpopulated area or the sea, to minimize human exposure. Randall described what might happen if New Horizons crashed into one's car in his what if? blog [1], and assuming the car was parked in the driveway the house would be similarly affected by the blast.

Luckily this was not what happened and when New Horizons reached Pluto 1½ month later Randall made this tribute to the achievement: 1551: Pluto and also on that day he released the first what if? in over three months, and it was called New Horizons.

Randall has used a Steve in a similar context in 809: Los Alamos (set in 1945). If this is the same person, then 'Steve' would be at least 90 years old in 2015. A person named Steve also comes up with an inappropriate suggestion in 1672: Women on 20s.


[Cueball and Ponytail are standing in front of a large computer console. Cueball's hands are on the keyboard; both are looking at the screen.]
Cueball: We made it! After all these years, New Horizons is finally revealing the surface of Pluto!
Ponytail: Take that, Dawn team.
[In the next four frames, we see photos, entirely black except for a circle in the middle. The circle is initially small, indistinct and appears in shades of grey. Successive circles are larger showing more color and shade variation. In the last, we see a blurry but recognizable outline of Africa, the Middle East and part of Western Asia, along with some clouds. The lighting pattern suggests that it is daytime in Africa, sometime in the northern summer.]
[A close-up of the two at the console.]
Cueball: OK, who did the calculations for the Jupiter slingshot maneuver?
Ponytail: (facing away from the computer console) Dammit, Steve...

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Anyone know why the text on the comic was heavily aliased (pixelated edges), although it's since been fixed on the xkcd website? Keavon (talk) 07:45, 1 June 2015 (UTC)

Probably a bad setting on the PNG compression by Randall when saving. Maybe he's trying to optimize file size (although in this case, the quality suffered). --BigMal // 11:53, 1 June 2015 (UTC)
Did the quality of the comic improve over time? Might have been a reference to the images provided by new horizons becoming more clear as it approached108.162.215.113 12:51, 5 June 2015 (UTC)
There's some weirdness in the earth images, too. You can see it if you bump the contrast and brightness a bunch -- there's a rectangular box around Earth, which it sits at the right end of. There's also a slight gradient in the box that's brighter at the right side, a couple of meandering green lines in the brightest part of the gradient, a series of green X shapes at lower left, and a repeating pattern of green, blue and pure black at top left. Curious, could be intentional or simply an artifact of how Randall made the image. 21:21, 22 June 2015 (UTC)

According to Wikipedia, "in August 2014, astronomers made high-precision measurements of Pluto's location and orbit around the Sun using the Atacama Large Millimeter/submillimeter Array to help NASA's New Horizons spacecraft accurately home in on Pluto." Was Steve involved in these measurements too? (And any of the numerous ways by which it can be determined how far away NH is and which way it is travelling!)--Laverock (talk) 12:43, 1 June 2015 (UTC)

This joke appears to be aimed at the implausibility of the Horizon Mission’s concept art, which looks suspiciously like earth. The image shows deserts, mountains and oceans which appear to be “riffs off” of a satellite image of the Horn of Africa, western Asia, and the Indian Ocean. Examples: Artist's conception of New Horizons at Pluto. Image Credit: NASA http://www.nasa.gov/sites/default/files/15-011a.jpg Image usage: http://www.spaceflightinsider.com/missions/solar-system/new-horizons-starts-first-phase-pluto-encounter/

I think that -is- Earth, a view of the probe right after it was launched. Then again... Classic Star Trek episode "Miri" is set on a distant planet with identical continents to Earth for no reason except to get you interested quickly. It was made before "Planet of the Apes" by the way (spoiler). An unsatisfactory novel called "Preserver" revisits it and proposes there are super-powered aliens just messing with us. Actually in Star Trek there are super-powered aliens just messing with us about every third week and they usually constructed their own gonzo planet just for that purpose, so the assumption that these are new, unknown super-powered aliens is unjustified, but of course true (The Preservers), unless they are really Organians or Q but they just don't say so. And if the Planet Copiers are abroad, who's to say that Earth is the original. Outside Trek, it's also even odds that a fictional Counter-Earth planet on the other side of the sun - there have been several although it's physically impossible - has identical continents to Earth. And in "D.R. and Quinch Have Fun On Earth", our continents are alien graffiti, unfortunately leading to cleanup. Love, Robert Carnegie [email protected] 11:17, 12 June 2015 (UTC)

I do not know if the image is concept art for the New Horizon mission from back in 2006; or if it is a more generic space exploration art work. It is hard to imagine that it is specific to the New Horizon’s Mission. One should ask New Horizons mission members to comment. There must be an interesting inside story. Dfh42 (talk) 15:49, 1 June 2015 (UTC)

This earlier mission art is probably closer to what Randall would consider plausible: http://www.nasa.gov/multimedia/imagegallery/image_feature_267.html Dfh42 (talk) 16:29, 1 June 2015 (UTC)

Waitasec, wouldn't the people on the ground know pretty much the exact position of this probe at all times? If nothing else they know its direction and distance from earth just by monitoring their communications with it. Odysseus654 (talk) 17:45, 1 June 2015 (UTC)

Yes, that is the joke.Zeimusu (talk) 21:18, 3 June 2015 (UTC)
Slingshot maneuver

It uses the gravity of a planet to alter the path and speed of a spacecraft. Reference I guess Steve miscalculated the maneuver. --Arturotena (talk) 06:41, 1 June 2015 (UTC)

I believe this really requires three bodies to work. The close passage by the small object slightly alters the orbital elements of the larger body (around the largest body, in this case, the sun), while also changing the orbit of the small body, both direction and speed.--DrMath 06:44, 27 May 2018 (UTC)

  1. Related tweet: As @NASANewHorizons gets closer, our view of #Pluto gets better and better!.
  2. Related link: NASA’s New Horizons Sees More Detail as It Draws Closer to Pluto.
  3. NASA Dawn Team

--Arturotena (talk) 06:34, 1 June 2015 (UTC)


If Pluto is 39.26 AU from the Sun, how can New Horizons be 0.34 AU from Pluto and 32.55 AU from the Sun? 20:54, 1 June 2015 (UTC)

I reinserted the sentence semi-major axis, and I added a Wikipedia link: semi-major axis. 21:47, 1 June 2015 (UTC)

Why is the distance even in the explanation ? -- I move to strike and delete Spongebog (talk) 15:02, 2 June 2015 (UTC)

No rotation and an imminent impact?

Most likely it's just a concession to making the cartoon easier to draw, but I'd note that between the third and fifth frames, Earth appears not to rotate noticeably. That implies either extreme speed, or less likely, slow enough speed that Earth is conveniently managing one or more complete rotations between frames. Since the conversation is implied to continue throughout, we can safely presume the former. That suggests an imminent collision somewhere on (or near) the southern coast of Yemen. 21:21, 22 June 2015 (UTC)


So is Steve a character now? What about a dwarf character? Z (talk) 20:22, 2 June 2015 (UTC)

There must be other people named "Steve" ! Spongebog (talk) 06:35, 3 June 2015 (UTC)
No, Steve was an only child . . . . BingoBash (talk) 06:45, 3 June 2015 (UTC)

Btw, Steve was also mentioned in comic 228. TronX7 (talk) 06:59, 5 June 2015 (UTC)

I didn't even see this as a representation of Earth. As I looked at each image, I thought I was seeing an image of Goofy (rather than Pluto) as seen through a glass orb. 20:26, 9 June 2015 (UTC)

I've fixed the three opaque links. I'll remove the incomplete tag in the next few days, unless anybody objects. Cosmogoblin (talk) 14:10, 24 June 2015 (UTC) (why are all the anonymous contributors on this page Californian? You're the other side of the country, you don't need to worry about NASA missions exploding!) added a link about the worst-case scenario in the event of a launch disaster, but just copied it from Wikipedia without checking - it was broken, so I searched for the source and fixed it. In doing so, I had a look at what the report says, and I'm not convinced the text from Wikipedia (sourced originally from "The Cosmic Compendium", ISBN 978-1329022027) is correct. The report indicates on page 4-30 that the scenario mentioned would result in "0.4 mean health effects", whereas a less likely scenario mentioned directly below that would result in "102 mean health effects", about 250 times worse. Still, it's from a cited, published source, and if anybody's wrong, it's Rupert W Anderson. Cosmogoblin (talk) 15:32, 26 June 2015 (UTC)

Cosmogoblin, the entirety of the text from "The Cosmic Compendium" by Rupert W Anderson is taken word for word straight from Wikipedia. So you didn't really chase your source far enough, I don't think. "Rupert" goes so far as to actually cite every single one of his sources as Wikipedia along with relevant licenses (public domain or creative commons) so I'm guessing that book is scamming people who don't realize what they're buying. (talk) (please sign your comments with ~~~~)