In 2015, NASA’s New Horizons spacecraft will zip past Pluto, giving us our first close-up view of this tiny world.

The team behind the space probe have a nice idea to help raise awareness of it: make a new US Post Office stamp commemorating it. My friend Dan Durda, both an accomplished astronomer and artist, created this lovely design of the stamp:

[Click to enhadesenate. Note: the word "Forever" means the stamp is always good for first class postage, and is crossed out here to prevent forgery.]

It shows the spacecraft going by Pluto and its (relatively) freakishly large moon Charon. I like how he didn’t go for photorealism, but instead used an oil paint-like feel for it. The stamp is meant as a followup — I might even say send-up — of a US stamp issued in 1990 about Pluto that has the label "Not Yet Explored".

I like this stamp! I’d love to see it made official, too. Alan Stern, the head guy for the mission, created a petition to help that along. It takes more than just a nice stamp design to get the PO’s notice; it has to have public support as well. I signed the petition, and if you want to, please do.

I’ll note that I expect this to raise the specter of whether Pluto is a planet or not. I have some thoughts on that, and I’ll be posting again soon on that topic.

This is pretty nifty: astronomers have discovered a fourth moon orbiting Pluto!

The tiny chunk of ice was found in Hubble images taken just a few weeks ago, and was clearly seen among the three previously known satellites:

It doesn’t have a name yet — it’s designated S/2011 P1 (or just P4 informally) — and it’s only about 13 – 34 km (8 to 21 miles) across. The size is estimated by measuring its brightness and assuming it’s icy like Pluto itself — a more reflective (white or icy) object would appear brighter than a darker object if they are the same size. Since its actual reflectivity isn’t known, the size has a wide range. But it’s still pretty dinky. For comparison, Pluto itself is 2300 km across, and its biggest moon Charon is well over 1000 km in size. I’ll note our own Moon is 3470 km across, so even Pluto is pretty small.

The thing is, in that single image above you can’t be sure if the object is a moon or a coincidentally placed background star. The solution: take a second image! That was done, clinching the moon’s identity:

See how it’s moved? Mind you, in the week or so between these two images Pluto moved substantially compared to background stars, and the moon moved along with it around the Sun at the same time it’s going around Pluto. You can see the motion of the other moons as well.

In the image, the diagonal lines are an optical effect inside the telescope itself. Pluto is very bright, so the astronomers used some processing techniques to make it appear much fainter, taking multiple images and subtracting one from the other to remove the glare of Pluto (it doesn’t work perfectly, which is why there is a black strip across the image; that blocks unwanted noisy light). I did this myself on many images when I worked on Hubble. It’s amazing how well it works, as you can see in the image above.

Mind you, Pluto was 5 billion km (3 billion miles) from Earth when this image was taken! But we’ll soon get much better pictures: the New Horizons probe will fly past the tiny world in 2015, snapping away as it does. We’ll probably learn more about Pluto in a few hours than we have since its discovery in 1930.

I wonder what they’ll name this iceball? The two moons Nix and Hydra (discovered in 2005) were named after Roman mythological characters associated with night time and Pluto. Cerberus seems like an obvious choice, but there’s already an asteroid with that name. Maybe they can change the spelling a bit to Kerberus to get around that. There’s already an asteroid named Persephone, too, if you’re curious. We’re running out of good names!

Well, whatever it’ll be called, it’s there, and we’ll see it up close in personal in just a few more years.

Credit: NASA, ESA, and M. Showalter (SETI institute)

In July 2015, the New Horizons probe will fly past Pluto, snapping pictures and taking data of this icy world. Whether you think Pluto is a planet or not^* it’s still a fascinating object and I can’t wait to see what New Horizons sends back.

But what happens after that? The space probe will still be traveling into deep space at high speed… but space out there isn’t empty. Beyond Pluto lie the solar system’s coldest denizens, the Kuiper Belt Objects. These are lumps of ice, frozen chunks that may take millennia to circle the Sun once. We’ve identified over a thousand of these KBOs, and there are tens of thousands more waiting to be discovered. Scientists with the New Horizons mission are hoping to find one near enough to the probe’s path to plan a flyby, so we can finally see one of these things up close.

And that’s where you come in!

A new website, Ice Hunters, has been put together to help you find potential KBOs for New Horizons to visit. It’s part of the Zooniverse; a citizen science project that gets people involved in real astronomy. In this case, you can examine images from the giant Magellan and Subaru telescopes to look for targets. It’s actually not terribly hard; here’s one image I looked at:

Basically, KBOs move over time, so two images are taken some time apart. One is digitally subtracted from the other, so stars tend to go away (though they don’t erase perfectly, leaving those ugly residuals). Any whitish blobs left are things that have changed between the two images: variable stars, asteroids, cosmic rays, and, hopefully, KBOs. When you find something you simply tag it by clicking it. A circle is placed around it, and the location is logged. You can see the object I found in the image above.

Humans are pretty good at this, while computers are easily confused by the messy residuals. But just to make sure every click is saved and compared to the work of other people. The more an object is clicked, the more likely it is to be something real and worth following up. The website explains how all this works.

That’s all there is to it! You have to register to do this (unless you’re already a Zooniverse member); it’s free and easy. And who knows? You may literally be the person who finds an icy world that will get a visit from New Horizons!

New Horizons image credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

^*My opinion: defining the word "planet" is a bad bet if not impossible. If you want the longer story, check out this article I wrote for Discover Magazine.

I follow the New Horizons Pluto probe Twitter feed, and recently it linked to a graphic showing where the spacecraft is right now:

Man, is that way out in the black. The probe is now closer to the orbit of Uranus than it is to Saturn, though both planets are over a billion kilometers away from New Horizons right now.

The solar system is frakkin’ BIG (if I may mix my colorful scifi metaphors). If you’re still not sure just how roomy things are out there, even at its current speed of 16.5 km/sec (10 miles/sec) — fast enough to cross the entire United States in five minutes — New Horizons won’t pass the orbit of Uranus until March 18, 2011, more than a year from now. Neptune’s orbit isn’t until August 24, 2014.

One thing to notice: from this point of view, planets revolve around the Sun in a counterclockwise fashion. Given the position of Pluto, you can see the two are heading for a close encounter soon. Well, for a sufficiently broad definition of "soon": July 14, 2015.

Space is big.

Today, December 29, 2009, the New Horizons Pluto probe crosses an arbitrary but psychologically important line: it is now closer to Pluto than it is to Earth.

If there were people on board the small interplanetary probe, no doubt they’d be popping champagne. I’m sure that back on Earth, the team behind NH are pretty happy. This probe has a checkered history, having been planned, canceled, re-planned, delayed, on and on. It’s amazing it got to launch at all. But on January 19, 2006 the small, half-ton probe was sent on its way, and on July 14, 2015 it’ll sail past Pluto and its collection of moons, snapping pictures and taking data.

Today marks the official halfway point, where New Horizons has half its path already behind it. Here’s a plot of its distance to Earth (in blue) and Pluto (red) care of the New Horizons site:

Distance in the graph is measured in Astronomical Units (a yardstick used by astronomers for convenience; it’s the distance of the Earth to the Sun, about 150 million km (93 million miles)). The distance to Earth is wiggly because the Earth goes around the Sun as New Horizons moves out, and the distance to Pluto decreases steadily as the spacecraft catches up on its journey. Where the two lines cross is where the distances are equal, and that’s now, today!

You may be wondering about the timing: New Horizons is halfway in distance to Pluto, but the mission timeline halfway point isn’t until October 16, 2010 (if I’ve done the math correctly). The probe was launched at high speed, slowed down due to the Earth’s and Sun’s gravity, picked up a kick from Jupiter in early 2007, and has been slowing ever since. Since it was moving faster before, it reached the distance halfway point before the schedule halfway point.

New Horizons is now 16.37 AU – 2.449 billion km, or 1.522 billion miles — from home. But maybe now, home is no longer Earth. Once it crossed that line today, home became deep space. Even Pluto and its moons Charon, Nix, and Hydra are only milestones for it. It won’t be stopping when it gets there; New Horizons will sail on by, continuing into deep space. It’ll become one of several other spacecraft we’ve sent out of the solar system itself, set to wander interstellar space forever.

That is, unless one day we catch up to them ourselves. I imagine in a few hundred years they’d make fine museum pieces. Or maybe, if poetry still exists in humans all those far-flung centuries from now, we’ll let those probes continue on. I rather like that idea better.

You can follow the New Horizons probe on Twitter, which is how I found out about this milestone today.

Art credit: ESO/L. Calçada

Speaking of web pages showing scale (OK, it was almost two weeks ago, but still cool), BABloggee Mike Sperry reminded me of this site which shows the solar system to scale… all on one web page! The Sun is displayed when you go to the page, and you can scroll to the right to see the planets, drawn in scale both in size and distance.

The Sun is about 560 pixels wide, putting Pluto something like 2 million pixels to the right. And some people wonder why it’ll take the New Horizons mission 9 years to get to Pluto…