by Paul Gilster | Mar 24, 2011 | Missions |
We have a long way to go before we can get a probe to another star in the space of a human lifetime. The figure always cited here is the heliocentric speed of Voyager 1, some 17.05 kilometers per second, which is faster than any of our outward bound spacecraft but would take well over 70,000 years to reach Alpha Centauri, assuming Voyager 1 were pointed in that direction. New Horizons is currently making 15.73 kilometers per second on its way to a Pluto/Charon flyby in July of 2015, impressive but not the kind of speed that would get us to interstellar probe territory.
Interestingly, the fastest spacecraft ever built weren’t headed out of the Solar System at all, but in toward the Sun. The Helios probes were West German vehicles launched by NASA, one in 1974, the other in 1976, producing successful missions to study conditions close to the Sun for a period of over ten years. The orbits of these two craft were highly elliptical, and at closest approach to the Sun, each reached speeds in the range of 70 kilometers per second. Helios II, marginally faster, lays claim to being the fastest man-made object in history.
It’s fun to juggle these numbers even as we think about how far we have to go before an interstellar probe becomes a possibility. If the goal is to reach Alpha Centauri with a mission lasting, say, forty years, then we need a tenth of lightspeed, or roughly 30,000 kilometers per second. That makes .10c a figure of distinction, because it creates a mission that can be built, flown and studied to completion by the same team. I’ve long argued that the goal of missions that could be completed within the lifetime of a researcher is one we’ll ultimately have to ignore, because for a time our deep probes beyond the system are going to take a much longer time than that. But get us to a tenth of c and that goal becomes possible, at least in terms of Centauri A and B.
Image: Smoke and steam fill the launch pad in January of 2006 as New Horizons roars into the blue sky aboard an Atlas V rocket. No craft ever had a faster Earth escape velocity, but the fastest spacecraft now exiting our Solar System is Voyager 1. Credit: NASA.
With the recent success of the MESSENGER probe in reaching Mercury orbit, it’s worth pointing out that another mission design from the Johns Hopkins University Applied Physics Laboratory (JHU/APL) would create a spacecraft even faster than the Helios probes. Like Helios, the Solar Probe Plus is headed for the Sun, with a goal of studying the outer corona. In its approach to within 8.5 solar radii (that’s just 0.04 AU), Solar Probe Plus would achieve a velocity of close to 200 km/sec, three times faster than Helios II. In interstellar terms, that works out to 6450 years to reach Centauri A and B, better than Voyager 1 but a numbingly long voyage even for a generation ship. Thus the difference between where we are now and where we would like to be.
New Horizons just passed the orbit of Uranus on March 18, described by an update on the mission site as “the fastest spacecraft ever launched.” And in a sense, that’s also true — New Horizons left Earth orbit traveling faster than any previous vehicle launched into interplanetary space. But the expected speed at Pluto/Charon encounter is about 14 kilometers per second, and it’s unlikely that any conceivable gravitational assist in the outer system could boost its speed to surpass Voyager 1’s. In any case, a recent tweet from the New Horizons team says there will be no Pluto gravity assist because it would impinge upon the scientific investigation of Pluto and its moons.
The good news, though, is that New Horizons should have enough fuel after Pluto encounter for one or even two Kuiper Belt Object flybys, targets that will not be selected until 2015. We thus keep our eyes on the coming flyby in the outer Solar System, with every indication that all is well aboard the spacecraft. A successful New Horizons should highlight yet another JHU/APL initiative, the Innovative Interstellar Explorer, a design intended to push out to 200 AU. Slowly, but with ever increasing steps, we’re learning our way around this Solar System and sketching out the regions beyond it. The propulsion challenges ahead are clearly defined, and energizing.
by Paul Gilster | Mar 23, 2011 | Deep Sky Astronomy & Telescopes |
With April approaching, my thoughts turn more and more to the release of the WISE data, which should tell us a great deal about brown dwarfs and other relatively cool objects in our stellar neighborhood. The Wide-Field Infrared Explorer mission hasn’t gained the media attention of a Kepler or a CoRoT because it’s not specifically a planet-hunter and isn’t in the business of turning up small, rocky worlds. But if you’ve been following our discussions here, you know how important a mission this is. We’ll get a bit more than half the data WISE has generated in April, and the rest of the dataset in 2012, by which time we may be able to identify, or else lay to rest the idea of, a gas giant (‘Tyche’) at 15000 AU, or a brown dwarf closer than Alpha Centauri.
It’s at the low end of the temperature range that so much interest is focusing these days, and the fact is that until we can get a read on how common brown dwarfs are, we won’t have a good idea about what kind of stars are most common in the galaxy. Until recently, the M-dwarf population, numbingly hot compared to the average brown dwarf, was assumed to be the most common stellar type, accounting for perhaps 75 percent of all stars. But we need to know the percentage of brown dwarfs, and to understand the various sub-groupings that make up this classification.
On that score, a binary system called CFBDSIR 1458+10, 75 light years from Earth, swims into interesting focus. Here we have two components, CFBDSIR 1458+10A and CFBDSIR 1458+10B, both of which are brown dwarfs, orbiting each other at a distance of about three AU with an orbital period of thirty years. The second brown dwarf (CFBDSIR 1458+10B) is now found to be perhaps the coolest star ever identified, with a temperature being reported on my side of the Atlantic as equivalent to that of a hot cup of coffee — in Europe, ESO is saying it’s as hot as a ‘freshly made cup of tea.’
So poke your finger in a nice, steaming cup of Costa Rica Tres Rios or a fine Darjeeling as the mood strikes you, and ponder a star of this temperature, just hot enough to bring water to a boil. What an intriguing object, as Michael Liu (University of Hawaii) is quick to note:
“At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets — it could even have water clouds in its atmosphere. In fact, once we start taking images of gas-giant planets around Sun-like stars in the near future, I expect that many of them will look like CFBDSIR 1458+10B.”
Liu is lead author of the paper on this work, where he and his colleagues point out that the object in question is 150 K cooler in temperature than any known brown dwarf, making it a candidate for the first member of the proposed Y spectral class. Thus far we just have models that suggest the presence of this class of ultra-cool brown dwarfs with temperatures below 500 K, although two recently discovered objects (UGPS 0722-05 and SDWFS 1433+35) have been considered possible members of the class. With a temperature of 370 K (plus or minus 40 K), the lesser dwarf in the binary Liu is studying would seem to be the best candidate yet.
From the paper:
Overall, CFBDSIR J1458+1013B is the most promising candidate to date for the hypothesized Y spectral class, given its extremely low luminosity, atypical near-IR colors, and cold inferred temperature. While spectroscopy is needed to place it in full context with the known T dwarfs, the singular nature of this object is unambiguous, thanks to our parallax measurement. CFBDSIR J1458+1013B is 1.5-2.0 magnitudes less luminous in the near-IR than any previously known brown dwarf and therefore is cooler than any known brown dwarf. For reference, two magnitudes in absolute magnitude spans most of the T dwarf sequence, from about T0 to T6… On this basis alone, this object is a significant leap.
Image: This image of the brown dwarf binary CFBDSIR 1458+10 was obtained using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii. Adaptive optics cancels out much of Earth’s atmospheric interference, improving the image sharpness by a factor of ten and enabling the very small separation binary to be resolved. This is the coolest pair of brown dwarfs found so far—the colder and dimmer of the two components is a candidate for the brown dwarf with the lowest temperature ever found. This color picture was created from images taken through four different filters at near-infrared wavelengths. Credit: Michael Liu, University of Hawaii.
Usefully, the orbital period is short enough that we will be able to estimate the mass of this binary system over the next few years, helpful information as we probe the limits of mass and star formation. Thus we explore that fascinating and blurry boundary between planet and star. In case you’re wondering, the proposed 370 K temperature for CFBDSIR 1458+10B is about 170 K higher than what John Matese and Daniel Whitmire are proposing for the temperature of Tyche, the hypothesized gas giant in the Oort Cloud. A blurry boundary between planet and star indeed.
The paper is Liu et al., “CFBDSIR J1458+1013B: A Very Cold (>T10) Brown Dwarf in a Binary System,” in press at The Astrophysical Journal (preprint).
by Paul Gilster | Mar 22, 2011 | Astrobiology and SETI |
An article in Time Magazine‘s latest issue caught my eye as I thumbed through it while waiting in line at the grocery store. The magazine is running a feature called ’10 Ideas That Will Change the World,’ and they tend toward being optimistic takes on huge problems. Thus the deficit gets an essay about how we’re going to fix it, while Afghanistan gets a thumbs-up for progress in the right direction. The article finds gold in everything from direct mailings (OK because they help charities raise money) to modern airports, which are creating a new kind of community.
And in the midst of this is a puzzling piece by Jeffrey Kluger called ‘Relax: You Don’t Need to Worry About Meeting E.T.’, where the upshot is: ‘Don’t worry about contact with extraterrestrial civilizations. It will never happen.’ Here’s a quote:
Humans and aliens haven’t connected yet, but with 1022 stars out there (that’s 1 with 22 zeros), it’s just a matter of time — right? Wrong. If exobiologists have learned anything, it’s that you and your kids and their kids’ kids will probably never hear the slightest peep from an alien. If E.T. the movie star is your idea of what extraterrestrial life might be like, you will be disappointed. If your thoughts run more to War of the Worlds, you can breathe easy.
Breathe easy? Let’s assume for a moment that Kluger is right, that contact with an extraterrestrial civilization is simply not going to happen at any time soon or in the future. If we knew that to be the case, would it be a cause for relief? For optimism? Maybe I travel with the wrong crowd, but most of us would be disappointed at the thought that we might never know whether intelligent civilizations exist around other star systems. Even those of us who think a confirmed SETI signal is unlikely any time soon — and I am one of these, believing that intelligent life is extraordinarily rare — would still hope to be proven wrong, and thrilled if we were.
Failure Is Not an Option
Kluger mentions both ‘E.T.’ and ‘War of the Worlds,’ so he’s not just reacting to disaster-oriented invasion films like ‘Battle: Los Angeles.’ The magazine seems to be implying that just the knowledge that we are either alone or unable to communicate with other civilizations is the solution to what Time bills as one of our worst problems. That phrase is used in the lead-in to these ten essays: ‘Our best shots for tackling our worst problems…’, of which knowledge of an alien culture is billed as number three on the list. And I’m wondering, since when is the idea of failing in our attempts to gain scientific knowledge considered the solution to a problem?
The essay goes through the difficulty in finding ETI, including our reliance on a sample of one to construct theories about life’s development on a planet, our uncertainty about how likely life is to develop even on worlds similar to our own, and the difficulty in finding an alien culture through SETI. That last point gets a quote from Don Brownlee (University of Washington), who notes the distances involved in going from star to star in the galaxy and says, “If the nearest hundred or thousand stars don’t have life, we probably won’t ever, ever, ever know about it anywhere else.”
That’s an interesting point if you strip it down to its basic assumptions. Picking up signals from a civilization something like our own would be a hugely difficult proposition even if they were being broadcast from a place as nearby as Centauri B. Pushing the distance out to a thousand light years makes things even more problematic. But we don’t know how long civilizations can exist, and the possibility of one living long enough to be thousands of years — if not millions — more sophisticated than our own can’t be ruled out. The factors that make a chance reception of a signal from a civilization like ours so tricky would be negligible to such an advanced species.
That possibility is one reason why we continue to look. And the fact that we have a sample of just one living planet to base our conclusions about life on is why we continue to look for life elsewhere, to broaden the sample and learn more about life’s mechanisms. So I don’t find any of this convincing in terms of making our detecting an alien civilization less likely to occur.
SETI, Distance and the Odds
But the point about stellar distances is still an interesting one. For one thing, we have a new paper by Joseph Catanzarite and Michael Shao (JPL) analyzing the Kepler science results that attempts to extract an estimate on how common Earth-like planets are. Let me quote from its summary:
Kepler’s science team has determined sizes, surface temperatures, orbit sizes and periods for over a thousand new planet candidates. Here, we show that 1.4% to 2.7% of stars like the Sun are expected to have Earth analog planets, based on the Kepler data release of Feb 2011. The estimate will improve when it is based on the full 3.5 to 6 year Kepler data set. Accurate knowledge of nEarth is necessary to plan future missions that will image and take spectra of Earthlike planets. Our result that Earths are relatively scarce means that a substantial effort will be needed to identify suitable target stars prior to these future missions.
We’re dealing with results that will be improved as the Kepler mission continues, but the figures so far cited indicate that planets like ours aren’t terribly common. Yes, it’s true that even with these low percentages, the option is still open for millions of Earth-like planets throughout the galaxy, given the sheer number of stars involved. But that other big imponderable — the question of how long civilizations last — still faces us. If they don’t tend to survive very long after they develop the ability to destroy themselves through technology, then Brownlee’s point has more resonance. And certainly these numbers say the nearest Earth-like planet may be a substantial distance away, a fact that will make studying it even more challenging than we first thought.
So yes, looking for ETI is difficult. But I can hardly share Kluger’s certainty in Time. He ends the essay, having looked at the possibility of alien extremophiles on Earth, by saying this:
Of course, even such aliens would hardly be the kind we either crave or fear — those who could regale us with tales of what things look like on the other side of the cosmos on the one hand, or conquer us with their superior intellects on the other. Too bad — or maybe very good — you’re never going to see them.
‘Never’ is a curious word to use in the midst of a great scientific investigation, one in which we hope to start assigning some reasonable values to the Drake Equation and find out just where we stand in terms of our place in the galaxy. We know so little, and Kepler and CoRoT are only the beginning of our space-based exploration of exoplanets increasingly like our own. We all have our views on this, and some of us are going to be proven wrong, but our investigations into extraterrestrial life are among the most energizing scientific projects in the history of our species. How could anyone possibly regard a failure to learn the answer as a good thing?
The paper cited above is Catanzarite and Shao, “The Occurrence Rate of Earth Analog Planets Orbiting Sunlike Stars” (preprint).
by Paul Gilster | Mar 21, 2011 | Outer Solar System |
Rains have come to the equatorial regions of Titan, a vivid marker of the changing seasons on the distant Saturnian moon. A large storm system appeared in the equatorial regions in late September of last year as spring came to the low latitudes, and extensive clouds followed in October. When they dissipated, the Cassini orbiter was able to capture surface changes in a 500,000 square kilometer region along the southern boundary of the Belet dune field, along with smaller areas nearby, all of which had become darker. The likely cause: Methane rain.
Tony Del Genio (Goddard Institute for Space Sciences) is a member of the Cassini imaging team:
“These outbreaks may be the Titan equivalent of what creates Earth’s tropical rainforest climates,” says Del Genio, “even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of Earth’s behavior over the tropical oceans than over tropical land areas.”
That’s an interesting take on these observations, because on Earth we find tropical bands of rain clouds year round in equatorial regions. On Titan, the evidence so far is telling us that extensive bands of clouds may occur in the tropics only during the equinoxes, bringing rain to what had been equatorial deserts. In fact, we’ve seen years of dry weather in the Titanian tropics, but now Cassini is showing us an area the size of Arizona and New Mexico combined that shows clear signs of saturation through a presumed methane rainfall that lasted several weeks.
Image: A huge arrow-shaped storm blows across the equatorial region of Titan in this image from NASA’s Cassini spacecraft, chronicling the seasonal weather changes on Saturn’s largest moon. This storm created large effects in the form of dark — likely wet — areas on the surface of the moon, visible in later images. After this storm dissipated, Cassini observed significant changes on Titan’s surface at the southern boundary of the dune field named Belet. The part of the storm that is visible here measures 1,200 kilometers (750 miles) in length east-to-west. The wings of the storm that trail off to the northwest and southwest from the easternmost point of the storm are each 1,500 kilometers (930 miles) long. Credit: NASA/JPL/SSI.
The changes in Titan’s weather over time are strikingly well defined. During the moon’s late southern summer back in 2004, major cloud systems were associated with its south polar region. The clouds seen in the 2010 imagery of the equatorial regions appeared one year after the August, 2009 equinox, when the Sun moved directly over the equator. The suggestion in this new work on Cassini data, which appears in Science, is that the global atmospheric circulation here is influenced both by the atmosphere and the surface, with the temperature of the surface responding more rapidly to changes in illumination than the thick atmosphere.
Thus we see Titan reacting to a change of seasons, though in delayed fashion, with an abrupt shift in cloud patterns that is reminiscent of what happens on Earth over tropical oceans rather than tropical land areas. Given these observations, the dry channels Cassini has seen in Titan’s low latitudes are likely caused by seasonal rainfall rather than being the remnants of a past, wetter era on the moon. Until this point in the Cassini mission, we had seen liquid hydrocarbons like methane and ethane only in the polar lakes of Titan, while the dunes of the equatorial regions were arid. Says Elizabeth Turtle (JHU/APL), lead author of the paper on this work:
“It’s amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite. These observations are helping us to understand how Titan works as a system, as well as similar processes on our own planet.”
The paper is Turtle et al., “Rapid and Extensive Surface Changes Near Titan’s Equator: Evidence of April Showers,” Science Vol. 331, No. 6023 (18 March 2011), pp. 1393-1394 (abstract).
by Paul Gilster | Mar 21, 2011 | Administrative
Tau Zero practitioners should be aware that deadlines on the following solicitations are approaching quickly:
(1) NASA Innovative Advanced Concepts (NIAC) – Early Stage Innovation
DEADLINE for Notices of Intent: 29-March-2011
(Just 7 workdays away)
DEADLINE for Proposals: 02-May-2011
(2) NASA Broad Agency Announcement (BAA): Technology Demonstration Missions (TDM)
DEADLINE for Notices of Intent: 31-March-2011
(Just 9 workdays away)
DEADLINE for Proposals: 31-May-2011
(3) NASA Broad Agency Announcement (BAA): Unique and Innovative Space Technology
DEADLINE for Exec Summary: 30-Sept-2011
DEADLINE for White Paper: 01-Nov-2011
DEADLINE for Proposal: 03-Jan-2012
