Dr. Alan Stern Answers Your Questions!

[/caption]Some of you may know, we recently launched a new “Ask” feature here at Universe Today. Our inaugural launch features Dr. Alan Stern, Principal Investigator for the New Horizons mission to Pluto and the Kuiper Belt. We collected your questions in our initial post and passed them along to Dr. Stern who graciously took the time to answer them.

Here are the questions picked by you, the readers, and Dr. Stern’s responses. We’d like to thank our readers for making this kick-off a success, as well as Dr. Stern for his participation.


1.) Many sci-fi authors have dreamed of putting some sort of telescope on the surface of Pluto to take advantage of the relative darkness and extreme cold encountered on this distant dwarf planet. How feasible would it be, judging from what we’re learning from the New Horizons expedition, to actually land a spacecraft, or a telescope, on Pluto’s surface? If such a telescope where deployed, how much more effective, if at all, could it be than an instrument like the JWST?

Alan Stern:“Space astronomy has revolutionized the way we look at the universe and is fundamental to modern astrophysics.” There are benefits to getting telescopes out of the atmosphere, and even benefits to getting out of Earth orbit, as in the case of Kepler and someday maybe JWST.

With regard to taking advantage of Pluto’s cold temperature – we’ve gotten really good at cooling down space telescopes. “There would be a benefit to placing a radio telescope on the far side of the Moon, but there’s no real practical reasons to place a telescope on Pluto—particularly given the cost of getting there, other than it being cool.”

2.) Kuiper objects differentiate strongly in color suggesting compositional or perhaps formation differences. Interestingly the color distribution correlates with the two different cold and hot Kuiper populations. Assuming the spectral analysis capability of New Horizon works for identifying the follow up Kuiper objects beyond Pluto-Charon, and given the putative possibility of choosing between several such targets, what type of target would the mission aim for? Would it try to cover as much diversity of objects as possible or is there a certain class of objects that could be important to concentrate on?

A.S: “We have to find Kuiper belt objects within our spacecraft’s fuel supply.” Stern elaborated, stating, “Predictions from our computer models tell us to expect to be able to have perhaps six possible candidates, to choose from, but so far we’ve just begun to search for these and though we’re finding KBOs, none we’ve found are yet are within the fuel supply.”

Stern also added, “Keep in mind our search for candidates isn’t easy – these are 27th magnitude objects which are roughly 50,000 times fainter than Pluto. What we’ll use to select between candidates once we have them are color, orbits, moons, rotational speeds – basically what combination of properties give us the most science for our fuel budget. The longer we wait after the Pluto flyby in July 2015 to make a decision, the more fuel will be consumed, so the “sweet spot” would be to have preliminary candidates in early 2015.”
(UT Note: New Horizons will perform its Pluto flyby in mid-2015 ).

3.) Given the limited funds available, Which do you recommend (Europa or Enceladus) as a suitable target for a mission in the 2025 time-frame in terms of value for money, scientific return, and practicality, and what kind of mission do you propose (lander vs. orbiter) ?

A.S: “Every scientist has their own judgment of what would make a good outer system flagship mission, or the best world to perform a series of missions that would equal a flagship mission.” Dr. Stern’s opinion is to explore Titan first, with Enceladus as a secondary target of that mission and Europa last, stating “Titan is the belle of the ball”, citing Titan’s active liquid cycle and thick atmosphere. Stern also added that he believes a mission to Titan would provide the most science per budget dollar.

4.) Four of the craft escaping the Solar System – Pioneers 10 & 11 and Voyagers 1 & 2 – have on board some sort of “message” to any possible extraterrestrials in the unlikely event they find it. Why was not some sort of message like that included on New Horizons, which may be the last (in our lifetimes) craft to also escape the Solar System?

A.S “There are several mementos onboard New Horizons, but no Voyager-like message.” Dr. Stern discussed a promise he made to his team that New Horizons would not be canceled and that he wanted his team focused on the science of the mission. Stern also pointed out that the process of deciding what to place on the Voyager plaques became mired in political correctness, (should the humans have been clothed? What cultures and races should be represented, etc.)

By separating the “icing from the cake”. Stern and his team have been able to concentrate on their main objective—to execute the New Horizons mission for about twenty cents on the dollar, as compared to the Voyager missions. Stern concluded with, “I’m proud that we got this done and that New Horizons is operating perfectly now way out there between Uranus and Neptune and flying almost a million kilometers per day toward the Pluto system.”

5.) Are any present or foreseeable technologies being considered for exploring the depths of our four “gas giant” planets?

A.S “There are no serious proposals to put a probe into one of the giant planets now, or even any call for such in the recent decadal survey for planetary missions. Keep in mind, though, that the Juno mission (now en route to Jupiter ) will use powerful remote sensing techniques to probe Jupiter from orbit around it to greater depths than the Galileo probe (which actually entered Jupiter’s atmosphere).”

6.) Why was it considered “urgent” to get to Pluto before the atmosphere refroze?

A.S “We have three “Group 1″ objectives for New Horizons. Map the surface, map the composition, and assay the atmosphere.” Stern referred to the objectives as a “three legged stool” in that no one objective could be omitted and still justify the mission, adding “so we need to accomplish that.. we need to get there before the atmosphere collapses”. Stern also referred to Pluto’s atmosphere as “very different from any other planet yet studied”, hence its inclusion as one of the three “Group 1” objectives.

7.) The Dawn mission to Vesta has shown us a body that was much less round than expected. Do you think it is possible that New Horizons will surprise us about Pluto, to the same degree? Please compare the expectations of the New Horizons fly by, to the early images of Vesta from Dawn.

A.S “With New Horizons being the first mission to Pluto, we will be surprised—after all, we’re always surprised on first reconnaissance flybys”. Stern added, “With Mariner 10, we discovered Mercury was all core, with Voyager we discovered volcanos and geysers across the outer solar system, and of course we were surprised when craters and river valleys were discovered by early Mars probes.”

Regarding Pluto, Stern stated “Pluto is the first discovered and soon to be reconnoitered of the most plentiful class of planets, while I’m not big on making predictions, I will say that what we will find will certainly be, well, wonderful.”

9.) Can new horizons now take more detailed photos of Pluto than HST? If not, when does it get close enough?

A.S “Great question! We actually thought about that a lot when designing New Horizons. One of our instruments, LORRI (Long-Range Reconnaissance Imager – http://pluto.jhuapl.edu/spacecraft/sciencePay.html) will provide us with views better than HST around April of 2015, and we expect to have about twenty weeks (10 weeks before, 10 weeks after the Pluto flyby) when we “own” the Pluto system — and I can guarantee the best images we hope to make should be as good as Landsat images of Earth!”

That wraps up our interview with Dr. Alan Stern. Once again, we at Universe Today would like to thank Dr. Stern for his gracious participation. If you’d like to learn more about the New Horizons mission to Pluto and The Kuiper Belt, visit: http://pluto.jhuapl.edu/index.php

Next month, we’ll be having an “Ask an Astronaut” feature with Mike Fossum, Commander of Expedition 29 on the International Space Station. Stay tuned!

Evidence of a Late Heavy Bombardment Occuring in Another Solar System

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Planetary scientists have not been able to agree that a turbulent period in our solar system’s history called the Late Heavy Bombardment actually occurred. But now, using observations from the Spitzer Space Telescope, scientists have detected activity resembling a similar type of event where icy bodies from the outer solar system are possibly pummeling rocky worlds closer to the star. This is the first time such activity has been seen in another planetary system.

“Where the comets are hitting the rocky bodies is in the habitable zone around this star, so not only are life-forming materials possibly being delivered to rocky worlds, but also in the right place for life as we know it to grow,” said Carey Lisse, senior research scientist at the Johns Hopkins University Applied Physics Laboratory. “This is similar to what happened to our own solar system during the Late Heavy Bombardment.”

Lisse spoke to journalists in a conference call from the Signposts of Planets meeting taking place at Goddard Space Flight Center this week.

Spitzer observations showed a band of dust around the nearby, naked-eye-visible star called Eta Corvi, located in the constellation Corvus in northern sky. Within the band of warm dust, Spitzer’s infrared detectors saw the chemical fingerprints of water ice, organics and rock, which strongly matches the contents of an obliterated giant comet, suggesting a collision took place between a planet and one or more comets. Also detected was evidence for flash-frozen rocks, nanodiamonds and amorphous silica.

This dust is located 3 AU away from Eta Corvi, which is the “habitable zone” around that star, and is close enough to the star that Earth-like worlds could exist. Lisse said although it hasn’t been confirmed, researchers think there is a Neptune-like world and at least two other planets in this system. A bright, icy Kuiper Belt-like region located 3-4 times farther out than our own Kuiper Belt was discovered around Eta Corvi in 2005.

“This is very possibly a planet-rich system,” Lisse said.

The light signature emitted by the dust around Eta Corvi also resembles meteorites found on Earth. “We see a match between dust around Eta Corvi and the Almahata Sitta meteorites, which fell to Earth in Sudan in 2008,” Llisse said. “We can argue that the material around Eta Covi is rich in carbon and water, things that help life grow on Earth.”

The Eta Corvi system is approximately one billion years old, which the research team considers about the right age for such a bombardment.

No asteroidal dust was found in the disk around Eta Corvi.

“Asteroidal dust would look like it had been heated, and chemically and physically altered, and most of the water and carbon would be gone,” Lisse said. “This dust is very rich in water and carbon and the rocky components are very primitive and un-altered.”

Most planetary formation theories can’t account for such an intense period of bombardment in our own solar system so late in its history, but the Nice Model proposed in 2005 suggests the Late Heavy Bombardment was triggered when the giant planets in our solar system— which formed in a more compact configuration – rapidly migrated away from each other (and their orbital separations all increased), and a disk of small asteroids and comets that lay outside the orbits of the planets was destabilized, causing a sudden massive delivery of asteroids and comets to the inner solar system. The barrage scarred the Moon and produced large amounts of dust.

“We can see the process of this happening at Eta Corvi and can learn more about our own solar system, since we can’t go back in time,” Lisse said. “It’s very possible that the rain of comets and Kuiper Belt Objects brought life to Earth.”

Lisse and his team are not sure if one big comet or lots of smaller comets are pummeling the inner solar system. “It is probably many bodies, but we only see the effects of the largest ones,” he said.

Could this be an indication that a Late Heavy Bombardment happens in many solar systems? “It’s not clear whether this is an atypical system, but we do know of one other possible system where it could be happening,” Lisse said in response to the question posed by Universe Today. “I think this is a rare event, which might mean that life is rare if you need a Late Heavy Bombardment for life to happen.”

Lisse said the reason they studied this star was the earlier detection of the Kuiper Belt-like region around Eta Corvi. “We knew it was an exceptional system from previous infrared sky surveys and the large bright Kuiper Belt was just the tip of the iceberg,” Lisse said. “This system was shouting, ‘I’m something extraordinary, come figure out my mystery!”

Paper: Spitzer Evidence for a Late Heavy Bombardment and the Formation of Urelites in Eta Corvi at ~1 Gyr

Source: Signposts of Planets conference call, JPL Press release

Pluto or Eris: Which is Bigger?

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The controversy between Pluto and Eris regarding their status as “largest dwarf planet” continues. During a joint meeting of the American Astronomical Society Division for Planetary Sciences and the European Planetary Science Congress last week in Nantes, France, new data was presented that may help settle the debate. The new findings regarding this size of Eris may be a surprise to some, and to others a confirmation of what was believed to be true.

How were astronomers able to make the new measurements of Eris, and what implications will these new measurements have on the Pluto / Eris debate?

Using a celestial alignment known as an occultation, Bruno Sicardy of the Paris Observatory (University of Pierre and Marie Curie, France) and his team were able calculate the diameter of Eris in 2010. The occultation was caused by Eris moving past a background star, which blocked the star’s light and cast a small shadow on Earth. When Sicardy and his team compared the shadow’s size at two different sites in Chile, the calculations provided a diameter of 2,326 kilometers for Eris. A previous study by Sicardy in 2009 placed Pluto’s diameter to be at least 2,338 kilometers.

However, the first estimates of Eris’ size that were made shortly after its discovery put the diameter at 3,000 km, plus or minus 400 km. But a later estimate from observations with the Hubble Space Telescope said Eris might be 2,400 km in diameter, plus or minus 100 km.

If Sicardy’s data calculations hold true, this places Pluto and Eris at nearly the exact same diameter. What has continued to not be up for debate, however, is that Eris is far more massive than Pluto. Given a nearly identical diameter for Eris and Pluto, Eris’s extra mass makes it the denser of the two dwarf planets. According to Sicardy and his team the increased density of Eris, “indicates that Eris is mainly composed of rocky material, with a relatively thin ice mantle.” Since Pluto’s density indicates it comprised of about equal parts ice and rock, Eris’s extra mass would appear to validate Sicardy’s assertion.

Eris and its moon, Dysnomia. Credit: NASA, ESA, and M. Brown (California Institute of Technology)

The Co-discoverer of Eris, and noted “Plutokiller” Mike Brown (Caltech) offers an interesting thought regarding the Pluto / Eris Debate:

“Scientifically, knowing which one is bigger will teach us…. absolutely nothing. The fact that they are nearly identical in size is scientifically interesting; which one is a few kilometers bigger than the other matters not one bit.” Brown also added, “But, still, I will admit to having a bit of an emotional attachment to Eris, so, deep down inside, I want to believe it will turn out to be a little bigger.

You can read a brief synopsis of Sicardy’s findings at: http://meetingorganizer.copernicus.org/EPSC-DPS2011/EPSC-DPS2011-137-8.pdf

If you’d like to learn more about the Pluto / Eris debate, Brown has some great thoughts regarding the debate on his blog at: http://www.mikebrownsplanets.com/2010/11/how-big-is-pluto-anyway.html

Help Scientists Decide on Which KBOs the New Horizons Spacecraft Will Visit

How would you like to help choose an additional destination or two for a spacecraft heading to the outer solar system? A new citizen science project from the Zooniverse — called Ice Hunters — will allow the public to help discover a potential new, icy follow-on destination for NASA’s New Horizons spacecraft, which is currently en route to make the first flyby of the Pluto system. However, after it zooms past Pluto, the spacecraft will have the capability to explore other Kuiper Belt Objects. But, the destination has yet to be chosen. That’s where you can help.

“Projects like this make the public part of modern space exploration,” said Dr. Pamela Gay. “The New Horizon’s mission was launched knowing we’d have to discover the object it would visit after Pluto. Now is the time to make that discovery and thanks to IceHunters, anyone can be that discoverer.”

With Ice Hunters, the public can help scientists search through specially-obtained deep telescopic images for currently unknown objects in the Kuiper Belt. While the images you’ll be perusing in Ice Hunters won’t be the beautiful astronomical images seen in the Galaxy Zoo classification of galaxies or the Moon Zoo images of the Moon, the science rewards in Ice Hunters will be spectacular.

And there’s more: there’s also the potential for discovering variable stars and asteroids.

What’s cool is that you’ll be searching for KBO’s and potential dwarf planets in much the same way that Clyde Tombaugh found Pluto: comparing images of the same region of the Kuiper Belt and looking for objects that move or vary in brightness.

“The New Horizons project is breaking new ground in many ways,” said New Horizons Principal Investigator Alan Stern. “We’re flying by a new kind of planet and we’ll be making the most distant encounters with planetary bodies in the history of space exploration, and now we’re employing citizen science to help find our potential extended mission flyby targets, perhaps a billion kilometers farther than even distant Pluto and its moons. We’re very excited to be working with Zooniverse and breaking this new kind of ground. We hope the public will be excited to join in with us and with Zooniverse to make a little history of their own by discovering our next flyby target after Pluto.”

Somewhere, on the outer edges of the solar system an icy body lurks undiscovered, orbiting on a path that will just happen to carry it toward a potential rendezvous with the New Horizons spacecraft.

New Horizons will flyby Pluto in 2015, and there will be enough gas in the spacecraft’s tank to fly toward at least one and possibly two Kuiper Belt Objects in the distant outer solar system. The expected date of the KBO flyby will be between 2016 and 2020, depending on the object chosen and its distance from Pluto.

Your mission, should you choose to accept, is to find the most interesting KBO possible for New Horizons to visit. If that object can be found , it will become the most distant object ever visited by a spacecraft from Earth.

The Kuiper Belt is a region of the outer solar system, extending past Neptune, (from 30AU) out to nearly twice Neptune’s orbit (out to roughly 55AU), which contains icy bodies in a variety of different sizes up to thousands of kilometers across. The first KBO other than Pluto was only discovered in 1992, and the KBO population is still not well mapped. Ice Hunters will do its part to study one small slice of the Kuiper Belt as it looks for an object along New Horizon’s trajectory after its Pluto flyby.

Using some of the largest telescopes in the world, scientists have imaged that region, producing millions of pictures for that could contain images of the rare objects that are orbiting toward just the right location, along with many other small worlds on different trajectories.

In “difference” images, which are created by subtracting observations taken at two different times, scientists can mostly (but not entirely) remove the light from constant sources like stars and galaxies. Left behind are the things that move or vary in brightness, which is what the users of IceHunters will be looking for. Since the stars never subtract off perfectly, the images appear messy, and computers can’t be trained to find objects as effectively as people can.

“When you’re looking for something special in masses of messy, real-world data, sometimes there’s no substitute for the human eye, and Zooniverse Ice Hunters will put thousands of eyes to work on this important job,” said John Spencer of Southwest Research Institute, a member of the New Horizons science team who is coordinating the search effort.

Just as other Zooniverse projects have easy-to-use websites, IceHunters.org is no different. “Using just about any modern web-browser, users can circle potential KBOs and mark with a star the locations of asteroids,” said web developer Cory Lehan from Southern Illinois University Edwardsville, who has participated in several Zooniverse web designs. “The website is filled with examples to help get people started. Anyone should be able to take part – No Flash required.”

So check out Ice Hunters and start discovering today!

You can follow Universe Today senior editor Nancy Atkinson on Twitter: @Nancy_A. Follow Universe Today for the latest space and astronomy news on Twitter @universetoday and on Facebook.

Q & A with Mike Brown, Pluto Killer, part 1

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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.

Also read our review of “How I Killed Pluto,” and find out how you can win a copy!

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!