MESSENGER's new solar system portrait, from the inside out
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Say cheese! The MESSENGER spacecraft has captured the first portrait of our Solar System from the inside looking out. The images, captured Nov. 3 and 16, 2010, were snapped with the Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) of MESSENGER’s Mercury Dual Imaging System (MDIS).
All of the planets are visible except for Uranus and Neptune, which at distances of 3.0 and 4.4 billion kilometers were too faint to detect with even the longest camera exposure time of 10 seconds. Their positions are indicated. The dwarf-planet Pluto, smaller and farther away, would have been even more difficult to observe.
Earth’s Moon and Jupiter’s Galilean satellites (Callisto, Ganymede, Europa, and Io) can be seen in the NAC image insets. Our Solar System’s perch on a spiral arm provided a beautiful view of part of the Milky Way galaxy, bottom center.
The following is a graphic showing the positions of the planets when the graphic was acquired:
The new mosaic provides a complement to the Solar System portrait – that one from the outside looking in – taken by Voyager 1 in 1990.
These six narrow-angle color images were made from the first ever 'portrait' of the solar system taken by Voyager 1, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic. The spacecraft acquired a total of 60 frames for a mosaic of the solar system which shows six of the planets. Mercury is too close to the sun to be seen. Mars was not detectable by the Voyager cameras due to scattered sunlight in the optics, and Pluto was not included in the mosaic because of its small size and distance from the sun. These blown-up images, left to right and top to bottom are Venus, Earth, Jupiter, and Saturn, Uranus, Neptune. The background features in the images are artifacts resulting from the magnification. The images were taken through three color filters -- violet, blue and green -- and recombined to produce the color images. Jupiter and Saturn were resolved by the camera but Uranus and Neptune appear larger than they really are because of image smear due to spacecraft motion during the long (15 second) exposure times. Earth appears to be in a band of light because it coincidentally lies right in the center of the scattered light rays resulting from taking the image so close to the sun. Earth was a crescent only 0.12 pixels in size. Venus was 0.11 pixel in diameter. The planetary images were taken with the narrow-angle camera (1500 mm focal length). Credit: NASA/JPL
“Obtaining this portrait was a terrific feat by the MESSENGER team,” says Sean Solomon, MESSENGER principal investigator and a researcher at the Carnegie Institution. “This snapshot of our neighborhood also reminds us that Earth is a member of a planetary family that was formed by common processes four and a half billion years ago. Our spacecraft is soon to orbit the innermost member of the family, one that holds many new answers to how Earth-like planets are assembled and evolve.”
Artist illustration of Eris and its moons. Image credit: NASA
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Here’s part 2 of our conversation with astronomer Mike Brown. Yesterday, he talked about the latest findings on Eris, the Haumea controversy and more; today he talks about being known as the “killer” of Pluto, his reflections on Brian Marsden and his hopes for the New Horizons mission to Pluto.
Universe Today: You seem to actually relish the role of Pluto Killer…
Mike Brown: You know, I didn’t initially. I really wanted to be the thoughtful person who explained to people what was going on and I tried very hard. And the reason I have become a sort of more militantly Pluto-killer-ish over the past couple of years is because — against what I think is reason — there are other astronomers who have been militantly pro-Pluto and saying things that are generally misleading in public. And it pains me to have scientists say things that I know they don’t actually think are true.
To hear an astronomer say that there is no logical reason why you would come up with eight planets, it makes no scientific sense. No one can say that and actually believe it. There are good arguments for one side or the other and I would enjoy it more if they would make the arguments instead of just trying to sort of manipulate public opinion, but I don’t think they do. Mostly the small number of the pro-Pluto crowd tends to be more manipulative. I thought somebody needs to defend the very reasonable idea of eight planets, so I have taken on that role.
UT: The Pluto-is-a-planet people are definitely vociferous.
Mike Brown: And honestly, I think manipulative is the word. They don’t believe what they say, they know what they say is not true and they say it in ways that are deceitful. That is maybe a strong statement to make, but they know what they are saying is not true. That bothers me. You shouldn’t say things that you know is not true just to make a point.
UT: Could you talk a little about Brian Marsden? He played a rather big role in the book, and in how things turned out with your discoveries – and the planet debate. He’ll obviously be missed.
Mike Brown: I have a book sitting at home that I had actually signed that I was going to send to him, and I didn’t get a chance to do it. I’m really sad that he didn’t get to see it. Everybody has their ‘Brian Marsden story’, and some are versions of the same story where he was incredibly supportive of interesting things in the solar system. When we started finding these large objects, there were a lot of people who were less supportive and not really happy about the discoveries. Brian was just happy about everything – if you were discovering new objects or comets, or different observations of asteroids – he just loved it all and he was always the first, you could just hear it in his voice when you talked to him, he was just genuinely excited about these new things that were being discovered.
He can’t be replaced. I like the people at the minor planet center and I like what they are doing, but he was unique. We won’t ever replace that energy and enthusiasm and the absolute love of the solar system that he had.
UT: How much are you looking forward to the New Horizons mission flyby of Pluto – and do you have any inklings of what it might come across in the Kuiper Belt?
Mike Brown. Credit: CalTech
Mike Brown: It going to be really interesting. The funny thing is, the answer to that question three weeks ago was “I can’t wait because all of these objects are sort of the same out there in the Kuiper Belt, and going to the closest one, even if it is not the biggest one will really teach you about everything that is out there.” That statement is no longer true. With Eris and Pluto being so different, we won’t learn as much about Eris as I had initially hoped, but like everyone else, I’ll be waiting anxiously for those first pictures to come back. I can’t wait to see them. Every time we go somewhere we’ve never gone before we learn things – the things we learn are never the things you think you are going to learn. I’m prepared to be astounded.
I am looking forward to, as much if not more perhaps, the later flyby of New Horizons of a small KBO. I think that scientifically understanding the smaller more typical objects is perhaps even more important than understanding the rare, big crazy objects.
Artist concept of the New Horizons spacecraft. Credit: NASA
UT: And are you still actively looking for objects out there?
Brown: Yes, we are looking very hard in the southern hemisphere now. We’ve finished the northern hemisphere, at least the bright objects, so I don’t think there will be too many more big ones discovered.
For the northern hemisphere, we knew that — at least — Clyde Tombaugh had been there first. We weren’t going to find something as bright as Pluto in the northern hemisphere because Clyde would have found it. In the southern hemisphere, it is basically wide open, because there was no Clyde Tombaugh, and we’re not even quite sure what the limit is. There’s not something 6th magnitude out there because someone would have seen it, but I don’t know how bright the brightest thing could be – that doesn’t mean that there’s something that bright there, but every day when we’re looking the possibilities are exciting.
UT: What telescopes are you using?
Brown: We have two that are working right now. One is actually an old data set from a near Earth asteroid survey and we are reprocessing the data in a way to make is sensitive to the types of objects we are looking for. This is the Uppsala ½ meter telescope at Siding Spring in Australia. It is the same telescope and the same data that the Catalina Sky Survey uses for the southern hemisphere.
And then as soon as telescope is finally online, we’ll use the Australian National University Skymapper telescope, which is kind of a Pan-STARRS south type of telescope that can do big surveys of the southern skies for many different purposes, including finding large Kuiper Belt objects.
It is fun to know again that some morning we might wake up and find something big and cool. That is always a fun way to go through life.
"How I Killed Pluto" -- a new book by planet hunter (and killer) Mike Brown.
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Talk about sticking to your convictions. Astronomer Mike Brown discovered an object that, at the time, was thought to be 27% bigger than Pluto. But he really didn’t want it to be a planet — he had argued against Pluto and other objects he had discovered being planets on the basis that they are in the middle of a “swarm” of similar objects. “To me it made no sense to pull one of even a few objects out of the swarm and call them something other than part of the swarm,” he wrote in his new book, “How I Killed Pluto and Why it Had it Coming.”
Universe Today had the chance to talk with Brown about his book, his discoveries, and even the latest news that perhaps Pluto actually is the biggest dwarf planet out there that we know of. Enjoy part 1 of our Q & A with Mike Brown, with part 2 coming tomorrow.
Universe Today: Over the past couple of weeks, some new discoveries have come out about the size of Eris. What are your thoughts that Pluto may actually be a bit bigger than Eris?
Mike Brown. Credit: CalTech
Mike Brown: The super-cool thing there is that when we first discovered Eris, it was great. I mean, it was fascinating for everyone in the public because we thought it was bigger than Pluto. But scientifically it really didn’t add much to our understanding of the solar system. Eris was kind of just a slightly larger twin of Pluto and nothing new was going on there. That was because we assumed it was near the larger end of the ranges of uncertainty. And by assuming that, we thought Eris was on the smaller end of density, making it the same density as Pluto. When that is the case, it is just a copy. But now that we realize it is essentially the same size as Pluto, that means Eris is a good bit more dense than Pluto, and that is actually really shocking. It tells you that these two things that formed in more or less the same place in the solar system and you would have predicted to have the same composition are essentially very different in composition. I’ve been beating my head against the wall ever since those first reports that Eris was actually smaller.
UT: Your new book, “How I Killed Pluto (and why it had it coming)” is a great read – a real page turner! How long did it take you to actually write your book?
Mike Brown: It was in fits and starts. I started it before the Pluto demotion, and I started it as sort of a ‘discovery of Eris’ book and when it looked like the IAU was going to declare it a planet. And then when it wasn’t a planet and when Pluto became part of the story I restarted it as still about Eris, but also about Pluto. In the end, the sad part of it that nobody really cares about Eris, they only care about Pluto, and so it took me awhile to get back to writing it and get to the point where I could say that this was really about Pluto as well as Eris. So it was over 2-3 years in different chunks, but the final part was a 6 month push in 2009 when I sat down and wrote the whole book.
UT: At the beginning of the book, you portray yourself as sort of stumbling into the field of looking for large objects in the Kuiper Belt. And yet here you are…
Mike Brown: I don’t know if there is any way to know ahead of time how your life is going to work out. Most people don’t have a grand plan they follow and have it work out. You start working on something and sometimes these things work out spectacularly; sometimes it works out OK, and nobody hears about it and sometimes things just don’t work out.
You see people who have done big amazing things, and you wonder how they got from here to there. Usually there is drive to do something, but everybody has to have some luck. They have to have drive and ability, as nobody does it on just luck, though. But there was no requirement that there were these large things out there in the outer solar system, and then the story would have been, “wow, what an idiot. This guy spent two years doing something and nothing came of it.” I had no way of knowing ahead of time which was going to be the answer. I’m lucky, and happy that it turned out the way it did.
Artist concept of Haumea. Credit: NASA
UT: There was a dispute about the discovery of Haumea, where either it was an incredible coincidence that other astronomers may have found the object, too, or they may have stolen your data. In your book you say that you’re fine with not really knowing what happened – which to me is incredibly noble of you (and I think you were very noble about the whole episode). Why don’t you want to know?
Mike Brown: I don’t mean to say I don’t want to know; I would love to know. If you knew the answer and I knew I could ply you with whisky until you told me, I would go out and buy as much whisky as I could. I would love to know the answer. I don’t think I ever will, and so I’m maybe resigned to that. In my gut, I feel like I know what happened, but I really don’t. I could be wrong and then every once in a while I have doubts and say maybe these guys really didn’t do anything wrong and they had their lives ruined. It is very frustrating. I really would like to know the answer because somebody in this story is a bad person, and I hope it is not me. But, god, what if it is?
UT: You certainly gave them the opportunity to tell their side of the story and I don’t know if they really have.
Mike Brown: No, they haven’t. And it is easy to take that interpretation, and if you watch enough “Law and Order” you know that people who hide what is going on are always guilty. But at the same time I try to put myself in their shoes, where they didn’t know what they were about to stumble into, and to suddenly be barraged by the media — to which they weren’t accustomed — and not knowing what to do about it, I can imagine that they wouldn’t tell their side of the story. If everything had been on the up and up, they may have behaved the same way. Deep down inside, I don’t think so, but I don’t have certainty. And I would love to have it. Someday, somewhere, someone may walk into my office and close the door and say, “OK, I know what happened and let me tell you.’ I relish that day, but I don’t know that it will ever happen.
UT: Well, again, I thought you were very nice about the whole episode.
Mike Brown: Before writing the book, I went back and looked at all the emails back and forth about this. The crazy part for me was that my daughter was 20 days old, and these guys had just potentially done something horrible. But when I started writing about it for the book, I didn’t really remember much of it because don’t think anyone remembers much from when their children are 20 days old. I could really only reconstruct it from my own emails with them. And looking back, I am kind of proud of myself. I was really very nice. I was very supportive. I made a big website proclaiming their discovery and pointing everything to them. So, wow, on lack of sleep I’m a relatively nice guy.
Perhaps it helps having a little infant that you are carrying around for perspective as far as what is important and what isn’t. As trite and cliché-ish as that is, I think it is actually true.
UT: But yet, you seem to relish the role of “Pluto Killer”…
Check back tomorrow to find out Mike Brown answers this question, and more!
"How I Killed Pluto" -- a new book by planet hunter (and killer) Mike Brown.
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It’s hard to imagine, but in 1992 astronomer Mike Brown didn’t know what the Kuiper Belt was. He had never heard of it. But just a few years later in 1999, he bet another scientist that within five more years he would find another planet out there at the edge of the solar system, past Pluto. It took a five-day extension of the bet, but Brown did it. And so began the death of Pluto as a planet, but the rise of a whole new class of objects called dwarf planets. Brown has written a book about his adventures as a planet hunter and eventual planet killer, called “How I Killed Pluto and Why it Had it Coming.”
His book is a highly readable, first person account of an astronomer who, by chance, realized he had remarkable penchant for discovering small, far away objects. The book is filled with humor, candor, geeky tendencies (he thought the first sonogram of his daughter looked like images from Venera 2 spacecraft from Venus), engaging personal anecdotes – and even romance, intrigue, mystery, fatherly love, and science.
“Discovery is exciting,” Brown writes in his book, “no matter how big or small or close or distant. But in the end, even better is discovering something that is capable of transforming our entire view of the sun and the solar system.”
And Brown’s discoveries have transformed our view of the solar system (some people have changed the world — how many can claim they have changed the solar system?!)
The discoveries of more objects in the Kuiper Belt turned on the heat of the debate of whether everyone’s favorite misfit planet, Pluto, was actually a planet or just a member of a new, quickly growing class of what are now called dwarf planets.
From this, some will claim, our planetary mnemonic went from “My Very Educated Mother Just Served Us Nine Pizzas” to “Mean Very Evil Men Just Shortened Up Nature.”
Mean and evil or educated? You decide.
Want a chance to win a copy of the book? Universe Today has 5 copies to giveaway!
UPDATE: We have winners! They are:
Gadi Eidelheit
Jason McInerney
Sten Thaning
Pam Jacobson
John Wenskovitch
Congrats!
Just send an email to [email protected] with the subject line of “Killing Pluto” by Monday, December 6 at 12 Noon Pacific Daylight Time. We’ll randomly choose 5 emails and notify the winners.
Eris — that pesky big dwarf planet that caused all the brouhaha about planets, dwarf planets, plutoids and the like — has gotten a closer look by a team of astronomers from several different universities, and guess what? Eris and Pluto have a lot in common. Eris appears to have a frozen surface, predominantly covered in nitrogen ice and methane, just like Pluto.
The scientists integrated two years of work conducted in Northern Arizona University’s new ice research laboratory, in addition to astronomical observations of Eris from the Multiple Mirror Telescope Observatory from Mount Hopkins, Ariz., and of Pluto from Steward Observatory from Kitt Peak, Ariz.
“There are only a handful of such labs doing this kind of work in the world,” said Stephen Tegler, from NAU and lead author of “Methane and Nitrogen Abundances on Eris and Pluto,” which was presented this week at the American Astronomical Society’s Divison of Planetary Science meeting. “By studying surfaces of icy dwarf planets, we hope to get a better understanding of the processes that affect their surfaces.”
NAU’s ice lab grew optically clear ice samples of methane, nitrogen, argon, methane-nitrogen mixtures, and methane-argon mixtures in a vacuum chamber at temperatures as low as minus 390 degrees Fahrenheit to simulate the planets’ cold surfaces. Light passed through the samples revealed the “chemical fingerprints” of molecules and atoms, which were compared to telescopic observations of sunlight reflected from the surfaces of Eris and Pluto.
“By combining the astronomical data and laboratory data, we found about 90 percent of Eris’s icy surface is made up of nitrogen ice and about 10 percent is made up of methane ice, which is not all that different from Pluto,” said David Cornelison, coauthor and physicist at Missouri State University.
The scientists say the recent findings will directly enhance NASA’s New Horizons spacecraft mission, currently scheduled to fly by Pluto in 2015, by lending greater value to the continued research of Eris and Pluto.
New Horizons image of Neptune and its largest moon, Triton. June 23, 2010. Credit: NASA
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This summer, the New Horizons spacecraft was awoken for its annual systems checkout, and took the opportunity to exercise the long range camera by snapping pictures of Neptune, which at the time, was 3.5 billion km (2.15 billion miles) away. The Long Range Reconnaissance Imager (LORRI) snapped several photos of the gas giant, but Neptune was not alone! The moon Triton made a cameo appearance. And the New Horizons team said that since Triton is often called Pluto’s “twin” it was perfect target practice for imaging its ultimate target, Pluto.
This image gets us excited for 2015 when New Horizons will approach and make the closest flyby ever of Pluto.
“That we were able to see Triton so close to Neptune, which is approximately 100 times brighter, shows us that the camera is working exactly as designed,” said New Horizons Project Scientist Hal Weaver, of the Johns Hopkins Applied Physics Laboratory. “This was a good test for LORRI.”
Weaver pointed out that the solar phase angle (the spacecraft-planet-Sun angle) was 34 degrees and the solar elongation angle (planet-spacecraft-Sun angle) was 95 degrees. Only New Horizons can observe Neptune at such large solar phase angles, which he says is key to studying the light-scattering properties of Neptune’s and Triton’s atmospheres.
“As New Horizons has traveled outward across the solar system, we’ve been using our imagers to make just such special-purpose studies of the giant planets and their moons because this is a small but completely unique contribution that New Horizons can make — because of our position out among the giant planets,” said New Horizons Principal Investigator Alan Stern.
Triton is slightly larger than Pluto, 2,700 kilometers (1,700 miles) in diameter compared to Pluto’s 2,400 kilometers (1,500 miles). Both objects have atmospheres composed mostly of nitrogen gas with a surface pressure only 1/70,000th of Earth’s, and comparably cold surface temperatures approaching minus-400 degrees Fahrenheit. Triton is widely believed to have been a member of the Kuiper Belt (as Pluto still is) that was captured into orbit around Neptune, probably during a collision early in the solar system’s history.
The Planet Pluto crossing in front of Barnard 92. Credit: John Chumack
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Last week, Pluto passed in front of what looks like a dark patch in the sky, and astrophotographer John Chumack was ready to capture the event. The dark patch is actually Barnard 92, a dark nebula. Since Pluto is usually very hard to see among the background of stars, it stands out against this dark nebula which blocks out the background stars. Still, Pluto – distant and dim as it is – is just a faint point of light, so John took special measures. “Although Pluto was easily visible in a short 5 minute exposure, I took an hour exposure to show the Dark nebula and the ‘rich & pretty’ surrounding star field,” he said.
The image was taken from John’s observatory in Yellow Springs, Ohio, using his homemade 16” Newtonian telescope and a QHY8CCD single shot color camera, captured from 01:00am until 02:00 am E.S.T. on July 6, 2010. Pluto and B92 sits within the large Sagittarius Star Cloud, M24.
Great shot, John! For more wonderful astronomical images, check out John’s website, Galactic Images.
New images of Pluto from the Hubble Space Telescope. Credit: NASA, ESA, and M. Buie (Southwest Research Institute).
Pluto-philes (and astronomers, too) have always bemoaned the fact that the best image of the principal dwarf planet wase just a fuzzy, pixelized haze. Bemoan no more. The most detailed look to date of the entire surface of Pluto has been constructed from hundreds of images taken by the Hubble Space Telescope. The images were taken during 2002 to 2003, and it took four years of computer crunching and software tweaking to create the global images. Surprisingly, the images show Pluto changed noticeably during the two-year photo shoot; the dwarf planet’s color became “redder,” and astronomers could see Pluto’s ice sheets were shifting.
“These Hubble pictures represent a true-color appearance of what you would see if you were near Pluto, comparable to looking at our own Moon with the naked eye,” said principal investigator Marc Buie of the Southwest Research Institute. “We now know we’re looking at something that has the biggest surface changes of any object in our solar system.”
The pictures show nitrogen ice growing and shrinking, getting brighter in the north and darker in the south.
Buie and planet hunter Mike Brown from Caltech introduced the Hubble images during a teleconference with reporters today, and emphasized how surprised they were with the changes seen on Pluto in just a relatively short period of time. Even accounting for seasonal changes, seasons can last 120 years in some regions of Pluto.
The top picture was taken in 1994 by the European Space Agency’s Faint Object Camera. The bottom image was taken in 2002-2003 by the Advanced Camera for Surveys. The dark band at the bottom of each map is the region that was hidden from view at the time the data were taken. Credit: NASA, ESA, and M. Buie (Southwest Research Institute)
They said the images underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes. While they believe the changes are driven by the seasons, it may mostly come from how quickly things can change on Pluto. The seasons are propelled as much by the planet’s 248-year elliptical orbit as its axial tilt — unlike Earth where the tilt alone drives seasons. On Pluto spring transitions to polar summer quickly in the northern hemisphere because Pluto is moving faster along its orbit when it is closer to the Sun.
“If Earth had such an extreme orbit, and we were experiencing a nice springtime day with 60-70 degree F temperatures, as the orbit changed it could suddenly drop to -90 degrees F,” said Brown.
There is also a mysterious bright spot on the center of Pluto, which has been observed in earlier images. But the spot is unusually rich in carbon monoxide frost.
The astronomers said Pluto is so small and distant that the task of resolving the surface is as challenging as trying to see the markings on a soccer ball 40 miles away. Buie said we won’t have a better look at Pluto until the New Horizon’s spacecraft is six months away from the dwarf planet in 2015.
The images were taken with the Advanced Camera for Surveys on HST, and the 348 images taken in 2002 and 2003 were the last ones taken of Pluto with high enough resolution to be useful. “I had time allocated two years ago to look at Pluto, which came just three or four weeks after the high resolution camera failed,” Buie. “That was very disappointing.”
But the images do show Pluto is significantly redder than it had been for the past several decades. Astronomers use the word “red” to mean it reflects more red light than blue or green light. To the human eye, Pluto has a yellowish-orange color, and is about 20% redder than it used to be. “It’s not as red as the surface of Mars, but more red than Io,” Buie said.
Red is usually associated with carbon. The astronomers said there is also methane, which is not usually stable in an environment like Pluto’s.
“This business about the color change had me scared for awhile,” Buie confessed. “I got the result years ago, but it was so hard to understand and believe. I’m still nervous about it. It could be that I completely screwed this up, but I can tell you Charon is on the same images, and Charon has the same color throughout but Pluto changed. I don’t’ know how the camera system on HST could have given me the wrong colors on Pluto.”
This was previously the best image of Pluto, taken in 2000 by HST. Credit: Eliot Young (SwRI) et al., NASA
Someone suggested that Pluto is reddening because of its recent demotion from full planethood. “Yes, people have said that Pluto is mad at me,” said Brown, who has the nickname of the “Pluto killer” because he discovered other Kuiper Belt objects which led to the new class of dwarf planets.
“For a long time Pluto was this lonely oddball that we didn’t have anything else to compare it with,” said Brown. “Understanding this all as a new class of objects is a much more interesting way of looking at the solar system and it is quite a bit of fun, too.”
Artist concept of the New Horizons spacecraft. Credit: NASA/JPL
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The New Horizons spacecraft crossed a milestone boundary today: it is now closer to its primary destination, Pluto, than to Earth. But New Horizons –the fastest man-made object — is not yet halfway to the dwarf planet. That won’t happen until February 25, 2010. New Horizons is now 1,440 days into its 9.5-year journey and well past 15 AU (astronomical units) from the Sun. But there is a long haul yet to go: there are still 1,928 days until operations begin for the close encounter, and 2022 days until the spacecraft reaches the closest point to Pluto in the summer of 2015. It is exciting to think what we will learn about Pluto and the Kuiper Belt in five and a half years. Will our perspectives change? Hard to believe they won’t.
New Horizons is currently traveling at about 50,000 kph (31,000 mph) (relative to the Sun) and is located about 2.4 billion kilometers (1.527 billion miles) from Earth.
The spacecraft launched in January 2006.
New Horizons will be taken out of hibernation in early January to repoint the communications dish antenna to keep up with the changing position of the Earth around the Sun. It was last awoken in November to download several months of stored science data from the Venetia Burney Student Dust Counter, to correct a recently discovered bug in the fault protection system software, (last thing anyone wants is to have the spacecraft go into safe mode at closest approach), and to upload instructions to run the spacecraft through early January. Telemetry shows that New Horizons is in very good health and almost exactly on its planned course.
Principal Investigator Alan Stern wrote in his last PI’s Perspective notes that the science team will meet in January to discuss which Kuiper Belt Objects they hope to “fly by and reconnoiter after Pluto. Those searches will begin next summer and continue through 2011 and 2012. Hopefully, they’ll net us four to 10 potential targets.”
New Horizons got a great shot of Neptune’s moon Triton last fall, as it was trucking toward Pluto and the Kuiper Belt.
The mission was 2.33 billion miles (3.75 billion kilometers) from Neptune on Oct. 16, when its Long Range Reconnaissance Imager (LORRI) locked onto the planet and snapped away. The craft was following a programmed sequence of commands as part of its annual checkout. NASA released the image Thursday afternoon.
Mission scientists say the shot was good practice for imaging Pluto, which New Horizons will do in 2015. Neptune’s moon Triton and Pluto — the former planet retitled in 2006 as the ambassador to the Kuiper Belt — have much in common.
“Among the objects visited by spacecraft so far, Triton is by far the best analog of Pluto,” said New Horizons Principal Investigator Alan Stern.
Triton is only slightly larger than Pluto, boasting a 1,700-mile (2,700-kilometers) diameter compared to Pluto’s 1,500-mile (2,400-kilometer) girth. Both objects have atmospheres primarily composed of nitrogen gas with a surface pressure only 1/70,000th of Earth’s, and comparably cold surface temperatures. Temperatures average -390 degrees F (-199 degrees C) on Triton and -370 degrees F (-188 degrees C) on Pluto.
Triton is widely believed to have once been a member of the Kuiper Belt that was captured into orbit around Neptune, probably during a collision early in the solar system’s history. Pluto was the first Kuiper Belt object to be discovered.
Furthermore, “We wanted to test LORRI’s ability to measure a faint object near a much brighter one using a special tracking mode,” said New Horizons Project Scientist Hal Weaver, of Johns Hopkins University, “and the Neptune-Triton pair perfectly fit the bill.”
LORRI was operated in 4-by-4 format (the original pixels are binned in groups of 16), and the spacecraft was put into a special tracking mode to allow for longer exposure times to maximize its sensitivity.
Mission scientists also wanted to measure Triton itself, to follow up on observations made by the Voyager 2 spacecraft during its flyby of Neptune in 1989. Those images revealed evidence of cryovolcanic activity and cantaloupe-like terrain. New Horizons can observe Neptune and Triton at solar phase angles (the Sun-object-spacecraft angle) that are not possible to achieve from Earth-based facilities, yielding new insight into the properties of Titan’s surface and Neptune’s atmosphere.
New Horizons is currently in electronic hibernation, 1.2 billion miles (1.93 billion kilometers) from home, speeding away from the Sun at 38,520 miles (61,991 kilometers) per hour. LORRI will continue to observe the Neptune-Triton pair during annual checkouts until the Pluto encounter in 2015.
LEAD IMAGE CAPTION: The top frame is a composite, full-frame (0.29° by 0.29°) LORRI image of Neptune taken Oct. 16, 2008, using an exposure time of 10 seconds and 4-by-4 pixel re-binning to achieve its highest possible sensitivity. The bottom frame is a twice-magnified view that more clearly shows the detection of Triton, Neptune’s largest moon. Neptune is the brightest object in the field and is saturated (on purpose) in this long exposure. Triton, which is about 16 arcsec east (celestial north is up, east is to the left) of Neptune, is approximately 180 times fainter. All the other objects in the image are background field stars. The dark “tails” on the brightest objects are artifacts of the LORRI charge-coupled device (CCD); the effect is small but easily seen in this logarithmic intensity stretch.(Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
