Moonrise

Image source with more information

In this image, arguably the most beautiful yet from New Horizons, Europa rises over the cloudtops of Jupiter.

All the best images from New Horizons' Jupiter encounter so far seem to have been in black and white, which I think is a small shame, given how colourful the planet and its moons are. It's understandable, though, because Jupiter is a radically different environment from Pluto. As mentioned in the caption for this colour image of Io:

[The Multispectral Visible Imaging Camera] is designed for the very faint solar illumination at Pluto, and is too sensitive to image the brightly lit daysides of Jupiter's moons.

A quick bit of maths* suggests that the sunlight at Pluto is about 64 times dimmer than at Jupiter (and 1600 times dimmer than at Earth). Of course, any images of Pluto would be fantastic, compared to the meagre, pixellated offerings that are all we have at the moment, but I think that New Horizons' snapshots of Jupiter are only a hint of what it will have to offer us when it eventually reaches the tenth** planet/second dwarf planet/first Kuiper Belt Object/possibly second Kuiper Belt Object including Triton [delete as appropriate].

*Earth is 1 Astronomical Unit from the sun (by definition), Jupiter about 5 AU and Pluto 40 AU (with a lot of variation). Solar flux decreases proportional to the inverse square - ie. if you were twice as far from the sun, you would receive a quarter as much sunlight. There's a nice explanation of this here.
**Don't forget Ceres!

The Future... in SPACE

While your tin-foil-suited life in a moon bubble may still be a long way off, there are some very exciting unmanned missions coming up over the next decade. All of the missions listed below have either already been launched or are launching this year.

Phoenix

Image source with more information

August 2007: Launch
May 2008: Land on Mars

Phoenix is the latest rover lander mission to Mars, and it's heading to a radically new environment from the ones we've seen from landers so far. Phoenix will land on Mars' northern polar region, looking to understand the history of the ice there (and thereby also the history of Mars' climate) and also to search for microbial life. On top of that it has a really nifty set of fan-like solar panels.
Phoenix homepage

New Horizons

Image source with more information

February 2007: Jupiter gravity assist
July 2015: Arrival at Pluto

New Horizons is the first mission to Pluto, and our first proper look at it. Next month, New Horizons will also become the latest mission to Jupiter, where it will hopefully do some science and get some pretty pictures. In the long run, New Horizons may also go on to visit other Kuiper Belt Objects.
New Horizons homepage

Dawn

Image source with larger version

Summer 2007: launch
March 2009: Mars gravity assist
September 2011: Arrival at Vesta
February 2015: Arrival at Ceres

Dawn is a spacecraft I find it easy to get excited about: a mission to Ceres and Vesta, the two largest bodies in the asteroid belt. Vesta seems to be a pretty standard potato as asteroids go, but Ceres is round enough to qualify as a dwarf planet and seems to have some interesting features, although we have no detailed images of it.
Dawn homepage

MESSENGER

Image source with more information

June 2007: Venus gravity assist
March 2011: Mercury orbit insertion

The only spacecraft so far to vist the Sun's innermost planet was Mariner 10, probably because not only is it really hard to get to, so far into the Sun's gravity well, but once you're there you have to worry about intense heat and radiation. MESSENGER looks set to give us a good look at a planet that's been off the guest list for too long.
MESSENGER homepage

Pink Moon

So I'm finally changing from the default templates towards something a little more personal. My webcomics links have taken a bit of a beating - I'll sort them out later. I'm sure you all recognise the world in the header image - it's certainly one of my own favourite moons. If I've never blogged about it before, it's simply because no-one has been there in about 17 years.

Triton is Neptune's largest moon - the third body in the solar system discovered to be volcanically active (after Earth and Io), and the second moon (after Titan) discovered to have an atmosphere (albeit a very thin one). One of the really intriguing things about Triton (aside from the fact that it's pink) is that it's very clear that it didn't form in its present neighbourhood, but instead was captured by Neptune after they had both formed. Add to that the fact that Triton seems very similar to Pluto (taking into account that we know relatively very little about Pluto at the moment) and that Pluto's eccentric orbit crosses Neptune's, and you have two worlds that are apparently siblings somehow.

Triton is the larger of the two, by the way. Just sayin'.

It may turn out, once we know more (for example, after New Horizons reaches Pluto), that Triton was the first Kuiper Belt Object we ever got a good look at. If you're interested in getting a good look at it yourself, the full version of the image I used can be found here.

Lakdawalla Corrals Robot, Quilt

Emily Lakdawalla is back at the Planetary Society Blog. Apparently she left to make a quilt. She's hardly been back, and she's already drawn my attention to a robot that I've missed: the MESSENGER mission to Mercury.

Louis D. Friedman covers the Bush administration's revised space policy. It's not as bad as you may have heard, but it's still made it clear that the Bush administration's first priority is to kick ass and take names - even in a vacuum.

Finally, in the interest of appearing fair and balanced, Bill Nye (who is apparently some famous science guy), in the last blog before Emily returned, turned out to be the only guest blogger who supports Pluto's (and hence a lot of other objects') status as a planet. Read.

Die Pluto, Die!

This week: John Spencer
John Spencer is a staff scientist at Southwest Research Institute's Department of Space Studies in Boulder, Colorado and is a member of the New Horizons [1] and Cassini [2] science teams. His research interests include the moons of the outer planets, particularly the Galilean satellites of Jupiter and the icy moons of Saturn. When he's not staring at a computer screen, he loves exploring Colorado's mountains with his wife Jane and their dog Maggie.

John Spencer has the definitive post on the whole "What is a planet?" deal, over at the planetary society blog. Now let us all play the sit-down-and-be-quiet game, please?

Alan Stern, head of the New Horizons mission (and therefore presumably John Spencer's boss) has other ideas. The lastest news item currently on the New Horizons website is an attack on the IAU's decision and a call to arms. Stern's opinion, expressed more eloquently in this article published shortly after the discovery of 2003 UB313, is that while Pluto's planethood was once opposed because it was considered a misfit, it is now opposed because we are beginning to realise that Pluto is in fact an exemplar of the bodies that make up the vast majority of the solar system.

I think the only sensible way to settle this 'debate' is... PRO-WRESTLING. 2003 UB313 Vs Jupiter, no holds barred! Hit it with the chair, Jupiter! Hit it hard!

Okay... Right

These past few days I've been a little out of sorts. I did manage to write 3000 words of monsterlicious story for Sunday Scribblings, but I faltered at the final scene and seem to be faltering at almost everything else as well. I'm feeling rather shaky and tearful, but I don't really have any good reason to be. I wish I could express myself better than that. Let's just say that I've chickened out this week.

Anyway, to lighten the mood, here are two humorous lists of top ten reasons why Pluto should/should not be a planet, courtesy of the Planetary Society.

This one has a nice nugget of truth in it:

8. When my son asks "Why is Pluto a planet, but Ceres isn't?" I want a better answer than "Old people are afraid of change."
Joshua B, Seattle, WA

(Although its accuracy is questionable - Ceres was demoted from planethood long before Pluto was discovered.)

This is the most rational reason for keeping Pluto a planet that I've heard:

3. It annoys people who like tidy categories.
Dennis D, Baton Rouge, LA

And the number one reason it shouldn't be a planet?

1. It doesn't appear to be so inclined.
Lyford R, Ventura, CA

Lyford R, you should be locked up for that one.

Oh No It Isn't!

Today the International Astronomical Union (IAU) decided that Pluto will not be keeping its "planet" title. Instead, Pluto, as well as asteroid Ceres and the larger-than-Pluto 2003 UB313 are now classified as "dwarf planets." According to the IAU, a "planet" is rounded by self gravity and has cleared its orbital zone, a "dwarf planet" is rounded by self gravity but has NOT cleared its orbital zone, and "small solar system bodies" are not rounded by self gravity. Because Pluto is part of the Kuiper belt and Ceres is part of the asteroid belt, neither has "cleared" its neighborhood, so they don't qualify as planets.

From the Planetary Society blog: It's Official: Pluto is NOT a Planet.

As it turns out, the proposed resolution that made so much notice when it was presented to the public last week -- and which would have expanded the solar system to 12 planets -- passed, but it was a different draft of the document in that it added the third criteria of a planet having to clear its neighborhood around its orbit.

Also from the Planetary Society: Pluto Gets the Boot - Solar System Shrinks to 8 Planets.

They also seem to have updated their excellent article on 'the new solar system' to include a section at the bottom entitled, Eight is Enough:

Even though it deprives him of the honor of being the discoverer of a planet, Michael Brown [one of the discoverers of 2003 UB313] likes the IAU resolution. If aliens came upon the solar system, he suggested on his website, "they would quickly come to the conclusion that there are 8 major bodies orbiting the Sun." Isn't it time, he argues, that we did the same?

My gut feeling is that creating a new category of 'dwarf planets' is a very sensible way to divide things up. Of course, that's not to say that the given definition of a dwarf planet is especially solid. Bad Astronomer Phil Plait has some criticisms of it here.

Finally, in an article entitled What’s in a Name? Explore ALL Worlds, says The Planetary Society we read that:

In response, Louis Friedman, Executive Director of The Planetary Society commented:

"The classification doesn’t matter. Pluto -- and all solar system objects -- are mysterious and exciting new worlds that need to be explored and better understood. Anytime we visit a new world -- planet, moon, asteroid, comet, whatever -- we make exciting and surprising new discoveries about the evolution of our solar system and about our own planet."

Yes, my idol, and one of the founders of the Planetary Society, Carl Sagan described our solar system as having hundreds of worlds, and I like that definition best of all.

Tran-Neptunian-Objects, We Hardly Know Ye

Here are some real images of two of the little (relatively speaking) round things that it's all about. Of course, being so little and, except in the case of Ceres, so far away, we don't have the most detailed images of them. That should partially change once the New Horizons probe reaches Pluto and Charon in about... nine years, I think.

Ceres:


Source with more information.

Pluto, the troublemaker:


Source with more information.

Clicking on the following three images will take you to the relevant page at the IAU website, where you can read an explanation and download a huge version. All the depictions of the 'new' planets and 'potential' planets in these images are artists impressions since we generally have even less detailed images of them than of Ceres and Pluto above.

The new solar system, everything to scale in terms of size, so you get an idea of how everything measures up:



The new guys, compared to some inner solar system planet that I can't quite recognise:



Guess who's coming to dinner? No, it's not Sidney Poitier, it's Quaoar! Start taking bets as to which of these guys gets to be lucky planet thirteen:

Twelve and Set to Rise

Given that my favourite worlds in the solar system are Jupiter's Galilean moons, you won't be surprised to learn that I don't really put much stock in the idea that being called ‘a planet’ is a necessary condition of being worthy of attention. It’s always seemed strange to me that people are happy to memorise the names of the ‘nine planets’, but will give you a blank stare if you mention Titan or Europa - despite the fact that these are two of the most intriguing bodies in the solar system.

But what is a planet anyway? Well, the word 'planet' comes from the Greek planetes, meaning wanderer (it's also the name of an excellent Japanese science fiction comic), and it was a name given to those 'objects that moved in the sky with respect to the background of fixed stars', as the IAU press release I link to below puts it. Obviously, that's a seriously dodgy definition, given that we can now observe loads of objects that fit that description.

What it comes down to is the fact that the nine things that we call(ed) planets aren't the only interesting things in the solar system. They are a good way to define the solar system in a big stroke - here are the significant bodies, most of the rest of the stuff is either orbiting them or in the asteroid belt here or the Kuiper belt here. The reason that Pluto isn't relevant in this broad definition is that we now know it to be only one example of a large number of similarly sized objects in the outer reaches of the solar system (the aforemention Kuiper belt in fact) - possibly as many as millions.

This poses a bit of a problem. It seemed that either we would have to accept that there are an enormous number of planets, a number that we can expect to keep growing indefinitely, or we would have to exclude the interloper from the club. Given that the first option turns a 'planet' from something significant to something that is mostly found in the Kuiper Belt, and the second, as Neil deGrasse Tyson reminds us gleefully, provokes squeals of horror from everyone under the age of twelve, it is perhaps not too surprising that the International Astronomical Union has attempted to take the middle road, as described in this press release:

If the definition is approved by the astronomers gathered 14-25 August 2006 at the IAU General Assembly in Prague, our Solar System will include 12 planets, with more to come: eight classical planets that dominate the system, three planets in a new and growing category of "plutons" - Pluto-like objects - and Ceres. Pluto remains a planet and is the prototype for the new category of "plutons."

The Planetary Society has an excellent news item on the history and reasoning behind this decision, which you can find here, and I highly recommend (with the power of the colour red) that you check it out if you want to be well informed on this subject.

Bad Astronomer Phil Plait, on the other hand, has an excellent criticism of the definition of a planet that the IAU is using:

The problem here is simple, really: we’re trying to wrap a scientific definition around a culturally-defined word that has no strict definition. Doing this will only lead to trouble. Why? For one thing, it’s divisive and silly. How does a definition help us at all? And how does it make things less confusing than they already are?

Adding:

There has been a lot of controversy about this, mostly in the media and the public, since most astronomers don’t care all that much.

In a similar vein, Sean of Cosmic Variance reminds us that we are not doing anything more than coming up with a definition for a word:

We are not doing science, or learning anything about the universe here. We’re just making up a definition, and we’re doing so solely for our own convenience. There is no pre-existing Platonic nature of "planet-ness" located out there in the world, which we are trying to discover so that we may bring our nomenclature in line with it. We are not discovering anything new about nature, nor even bringing any reality into existence by our choices.

To an extent, I am ambivalent about this. On the one hand, I strongly felt that we should have just knocked Pluto back and set the number at eight. But on the other hand, I like the fact that this draws attention to all the other interesting bodies in the solar system. I wonder how many people had even heard of Ceres before now?