Tag: planet

A fifth moon for Pluto!

By Phil Plait | July 11, 2012 10:12 am

Astronomers have just announced that tiny Pluto has a fifth moon! It was discovered using the Hubble Space Telescope:

You can see it in that image (click to enhadesenate) in the green circle. Pluto was targeted by HST for several observations in late June and early July, and P5 – also called S/2012 (134340), the moon’s designation until it gets a proper name – was seen moving around the tiny world. This image is from July 7.

As moons go, it isn’t much: it’s probably only about 10 – 25 kilometers (6 – 15 miles) across, making it one of the smallest moons detected in the entire solar system. That’s actually pretty amazing, given Pluto was 4.7 billion km away (2.8 billion miles) when these images were taken!

Pluto was observed in part to look for more moons. In 2015, the New Horizons probe will zip past Pluto, and scientists want to know as much about the system as they can before it gets there. The odds are low of them hitting any of those moons – space is big, and the moons and spacecraft are small – but a) better safe than sorry, and 2) if there are more targets to observe we want to know now so they can be added to the itinerary!

Observations like this are good for discovering moons and getting their locations, but size is a different matter. Literally. We know how far away the moon is, and how bright, but it’s far too small to directly get the size. Its diameter has to be estimated by assuming how reflective the surface is. If it’s dark like coal, it has to be bigger to be so bright, and if it’s shiny like ice, it’s smaller. That’s why we don’t know P5′s size to even within a factor of 2! But once New Horizons zips past, it may be able to nail down the size far better.

The first moon of Pluto, Charon, was discovered in 1978. Nix and Hydra were found using Hubble in 2006, and the fourth moon just last year, in 2011.

As for the argument about Pluto being a planet or not, this will no doubt provide grist for the mill. However, number of moons does not a planet make; Mercury and Venus have none and they’re planets. Mars has twice as many as Earth does, but it’s not twice the planet! And many very small asteroids have moons, too.

My feelings about this are on record: the word "planet" is not and can not be defined; it’s a concept, not a definition. It’s like the word "continent": it’s more of an idea than something you can rigidly define. There is no sharp border that you can use to divide objects into planet and not planet.

So I actually don’t care if you call Pluto a planet or not. It is what it is: a very cool object, perhaps the biggest in the Kuiper Belt of frozen icy comet-like bodies past Neptune. It’s an oddity, since it’s so bright, and yes, has so many moons.

And it’s absolutely worthy of study, no matter what you call it.

Image credit: NASA, ESA, and M. Showalter (SETI Institute)

Related Posts:

- Pluto has another moon!
- The unbearable roundness of being
- BAFact math: How bright is the Sun from Pluto? (and the followup, How big does the Sun look from Pluto?)
Shining shoes for NASA

Blastr: So, you wanna blow up the Earth?

By Phil Plait | September 13, 2011 1:00 pm

Blowing up a planet is hard. Really, really, really, really hard. In fact, if you had one "really" in that sentence for every Joule of energy it would take to make the Earth all explodey, you’d need more than 2 x 1032 of them. That’s a lot of "really"s.

I actually calculated that number using some basic physics and math, and then decided to write an entire article around it, which is now up on Blastr. It doesn’t matter how big a supervillain you are, blowing up a planet is next to impossible, despite the non-existence of Ceti Alpha 6.

There are ways of tearing a planet apart, actually, but I didn’t want the article to go on too long, and I figure exploding one versus ripping it apart are different things. Maybe I’ll do a follow up article. And really, why blow it up at all? If you want to kill everything on it, just set up a massive ad campaign for hair spray, sell the inhabitants a billion cans of the stuff, and then sit back and wait for them to destroy their ozone layer. Done and done.

[P.S. Today marks the 12th anniversary, ironically, of the Moon being blasted out of Earth orbit. Happy Breakaway day!]

Related posts:

- Blastr: My Favorite TV Scientists
- Blastroid
- Blastr: Other than that, Spock, how was the movie?
- Blastr: I Was A Zombie For Science
- Big budget movies that got their science right
- Master of Blastr

MORE ABOUT: Blastr, planet

No, there's no proof of a giant planet in the outer solar system

By Phil Plait | February 14, 2011 2:30 pm

I’m getting a lot of email and tweets about NASA supposedly having proof of a giant, Jupiter-sized planet orbiting the Sun way beyond Pluto. Let me be clear: while certainly possible, this idea is not at all proven, and in my opinion still pretty unlikely. As usual, this started as a more-or-less accurate media story and is getting inflated as it gets re-reported. As far as I can tell, the original report was in the UK paper The Independent.

Here’s the deal. Two astronomers, John Matese and Dan Whitmire, have theorized about the possibility of a previously-undiscovered planet way beyond Pluto for some time. This is not a crazy idea; we see planets orbiting other stars way out, and there’s other evidence big planets can be pretty far out from the Sun (mind you, evidence does not mean proof). As it happens, there are lots of chunks of ice orbiting the Sun pretty far out as well. Some of these have orbits which bring them into the inner solar system, and we see them as long-period comets.

What Matese and Whitmire did was wonder how a big planet would affect the orbits of these comets. If you measured enough of them, would you see the effects of the gravity of this planet? They claim you can, and even gave the planet a tentative name: Tyche.

I read their papers, and thought the data were interesting but unconvincing. The sample size was too small. A bigger study was done, but again the effects weren’t quite enough to rise to the level of breakthrough. I’m not saying the astronomers are wrong — the data were certainly provocative, and potentially correct! Just not firm enough. Read More

CATEGORIZED UNDER: Astronomy, Piece of mind, Skepticism
MORE ABOUT: comets, planet, Tyche

Possible earthlike planet found in the Goldilocks zone of a nearby star!

By Phil Plait | September 29, 2010 4:37 pm

Astronomers have announced the discovery of a planet with about three times the Earth’s mass orbiting the nearby red dwarf star Gliese 581. That in itself is cool news; a planet like that is very hard to detect.

But the amazing thing is that the planet’s distance from the star puts it in the Goldilocks Zone: the region where liquid water could exist on its surface!


Artist’s drawing (from 2007, before this announcement) of the planetary system of Gliese 581. Credit: ESO

First, a few things: 1) Gliese 581 is a dinky, cool red dwarf about 20 light years away. That’s pretty close as stars go; only a handful are closer. Bear in mind it’s still 200 trillion kilometers (120 trillion miles) away, and that’s still a bit of a drive.

2) The planet is one of six now known to orbit the star [that link goes to a PDF of the journal paper]. Apparently, all the planets have neat, circular orbits, so the system seems to be stable. This new planet takes 37 days to orbit the star once, and orbits at a distance about 1/6 the distance of the Earth from the Sun. As far as we know, it’s the fourth planet from its star.

3) The planets have all been found by the Doppler method: as they orbit the star, they tug on it. This causes a shift in the wavelength of emitted light from the star. The mass of the planet, its distance from the star, and the shape of the orbit all determine how the light shifts, which is how astronomers found those properties of the new planet.

OK, so that’s what we know. Now let me be clear here about stuff we can be fairly sure about.

Read More

CATEGORIZED UNDER: Astronomy, Cool stuff, Top Post

Astronomers see exoplanet orbiting its parent star!

By Phil Plait | June 10, 2010 12:00 pm

This is extremely cool news: astronomers have, for the first time, directly seen an exoplanet orbiting its star from one side to the other!

Here’s the incredible picture:


This makes me happy scientifically, of course, but also for personal reasons. Let me tell you a story. Two, in fact…

1) [Story the First] Beta Pic: the star, the planet, the disk

The star in question is Beta Pictoris (or just Beta Pic to its friends), a very young star — it’s only a few million years old, compared to the Sun’s advanced age of 4.56 billion — with about twice the Sun’s mass and 9 times its brightness. As stars go, Beta Pix is pretty close, just 63 light years away, and is easily bright enough to be seen with the unaided eye from the southern hemisphere.

In the above picture, taken using one of the European Southern Observatory’s ginormous 8.2 meter units of the Very Large Telescope, Beta Pic is represented by the dot in the center. The star is so bright its light swamps everything around it, so the star itself has been blocked by a piece of metal inside the camera that took the shot (that’s the reason for the dark circle in the center of the picture) so the astronomers subtracted the image of a nearby star to minimize the effects of the light from Beta Pic itself; this is a common technique I’ve used myself in Hubble images*. This allows us to see much fainter stuff near the star.

This picture is actually a composite of three separate observations. The outer part with the blue fuzzy stuff was observed in 1996, and I’ll get back to that in a sec. The good stuff is in the center: two images of the planet, called Beta Pic b, are superposed in the picture; it was observed in 2003 (left blob), then again in late 2009 (right blob). Observations taken just months before in 2008 and 2009 observation didn’t show the blob at all — it must have been too close to the star to be seen clearly — indicating this really is a planet orbiting the star, and not just some background object like a star or galaxy. In other words, astronomers have captured the motion of the planet as it physically moved from one side of the star to the other!

Read More


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