by Paul Gilster | Jan 30, 2009 | Outer Solar System |
Rain seems to have been plentiful at Titan’s south pole. A new analysis of Cassini imagery compares the region in recent times with what it was about a year earlier, noting new features in areas many scientists believe to be lakes of liquid hydrocarbons. Adding to the conjecture is the fact that extensive cloud systems covered the region during this period, evidence for a large rainstorm amid changing seasons. All this comes from the almost global surface map Cassini’s Imaging Science Subsystem has been acquiring since April of 2004.
Have a look at some of this imagery, and keep an eye in particular on Ontario Lacus, at the bottom of each image, noting the difference in brightness.
Image (click to enlarge): The images on the left (unlabeled at top and labeled at bottom) were acquired July 3, 2004. Those on the right were taken June 6, 2005. In the 2005 images, new dark areas are visible and have been circled in the labeled version. The very bright features are clouds in the lower atmosphere (the troposphere). Titan’s clouds behave similarly to those on Earth, changing rapidly on timescales of hours and appearing in different places from day to day. During the year that elapsed between these two observations, clouds were frequently observed at Titan’s south pole by observers on Earth and by Cassini’s imaging science subsystem. Credit: NASA/JPL/Space Science Institute.
We now watch to see what happens as summer approaches in Titan’s northern ‘lake district.’ The Cassini team has released an updated map that includes near infrared images of a part of this area, adding to observations from other Cassini instruments that show greater amounts of liquid methane in the northern hemisphere than the southern. By all accounts, then, things should get active up north as the seasons progress. An active weather cycle with convective cloud systems and plentiful precipitation may well be the result, probably in amounts larger than we’ve documented so far in the south.
A Cassini news release covers the release of the latest map and goes on to point out an interesting fact: Although some of the northern lakes are quite large — Kraken Mare, if full, would be five times the size of Lake Superior — evaporation from the surface cannot account for the replenishment of the atmospheric methane lost through rainfall and surface deposition of haze particles. Elizabeth Turtle (Johns Hopkins Applied Physics Lab) explains:
“A recent study suggested that there’s not enough liquid methane on Titan’s surface to resupply the atmosphere over long geologic timescales. Our new map provides more coverage of Titan’s poles, but even if all of the features we see there were filled with liquid methane, there’s still not enough to sustain the atmosphere for more than 10 million years.”
That points to underground reservoirs of methane amidst a terrain filled with interesting organic chemistry. Even so, how long can this atmosphere persist? Another question is why we find liquids collecting in the polar regions and not at the lower latitudes. One thing on Cassini’s future agenda will be the study of clouds and temporary lakes near the equator as peak sunlight shifts in the spring and fall. For more, see Turtle et al., “Cassini imaging of Titan’s high-latitude lakes, clouds, and south-polar surface changes,” Geophysical Research Letters 36 (29 January 2009), p. L02204 (abstract).
by Paul Gilster | Jan 29, 2009 | Deep Sky Astronomy & Telescopes |
Just how common are brown dwarfs? The answer is still up for debate, for stars like these (with masses less than 0.05 that of the Sun) are so small that they do not burn hydrogen, and as they age, they become more and more difficult to detect. But we’d like to know more, especially in understanding our local interstellar neighborhood. Red dwarfs are common throughout the galaxy, and we know that they can support planetary systems and even worlds in the habitable zone. Is it possible that brown dwarfs are even more numerous than red dwarfs?
Asking questions like these takes us into what is known as the initial mass function (IMF), which involves the number of stars versus their masses at the time of their formation. The place to study the issue is a star forming region like the one shown in the image below. This Subaru Telescope composite shows the W3 Main region, about 6,000 light years away in the constellation Cassiopeia. A region like this is helpful because the majority of stars within it formed at roughly the same time, unlike a more random sampling of stars from elsewhere.
Image: Tricolor composite image of W3 Main where massive stars are being born. Red colored objects to the left of center are extremely young massive stars, surrounded by less massive stars of one million years old. Nebulae with a variety of colors and appearances are ionized gas reflecting light from these stars. Filamentary dark clouds are also conspicuous. The line at bottom left shows a scale of 0.2 parsecs, which is approximately 40 thousand astronomical units. Credit: Subaru Telescope/NAOJ.
Low-mass star forming regions like Taurus may skew the broader picture, for it’s not known whether clusters of massive stars would show the same proportion of smaller stars among them. Thus the need for the Subaru study of W3 Main, which produced an image the observatory is calling “…the deepest and finest image from a ground-based telescope among the images of massive star forming regions.” The work points to a substantial number of brown dwarfs in the region. But it also finds that this distribution is significantly different from regions like the Trapezium cluster and IC 348, where a much smaller percentage of brown dwarfs have been identified in earlier studies.
Image: Stellar census showing population according to weight. The horizontal axis is the mass in the unit of the solar mass in log scale, while the vertical axis is the number of stars in log scale. In the W3 Main region (thick line), the population increases toward the less massive stars down to brown dwarf masses, indicating the abundance of the brown dwarfs in this region. Note that the turn over is in the more massive range in the Orion Trapezium cluster region. Credit: Subaru Telescope/NAOJ.
Our brown dwarf question, then, is still unanswered, but we’re making progress. This paper, which is to run in February in the Astrophysical Journal, takes our study of the initial mass function down below the hydrogen burning limit, and points to future work that will help us determine the prevalence of brown dwarfs in our galaxy. The paper is Ojha et al., “Young Brown Dwarfs in the Core of the W3 Main Star-Forming Region,” available online. A Subaru Telescope news release is also available.
by Paul Gilster | Jan 28, 2009 | Exoplanetary Science |
I absolutely love the image below, so I decided to run it at full size although it doesn’t quite fit the column width. You’re looking at the result of recent work from the California & Carnegie Planet Search team, which used data from the Spitzer Space Telescope to produce what is probably the most accurate image yet of an exoplanet. It’s not an actual photographic image, of course, but it’s better than an artist’s interpretation because it’s based on highly realistic simulations.
The planet in question is HD 80606b, which circles a star about 200 light years from Earth. This is a highly interesting place, some four times the mass of Jupiter and moving within a 111-day orbit around its star. What makes it stand out is the incredible eccentricity of its orbit. We’re talking about a world that for most of its orbit is at distances that would be between Venus and Earth here in our system. But then it swoops in ever closer to its primary until it closes to within 0.03 AU, an encounter it experiences for less than a day.
Image: The planet HD80606b glows orange from its own heat in this computer-generated image. A massive storm has formed in response to the pulse of heat delivered during the planet’s close swing past its star. The blue crescent is reflected light from the star. Credit: D. Kasen, J. Langton, and G. Laughlin (UCSC).
The Spitzer observations took place during this period of closest approach, when a secondary eclipse (as the planet passed behind the star) allowed precise measurements that the researchers used to peg the temperatures on this world. To describe what happens at perihelion, I turn to Jonathan Langton, a UCSC postdoc, who discussed the matter in this news release. HD 80606b is, as you might imagine, a place of storms that defy the imagination, and planetary shockwaves:
“The initial response could be described as an explosion on the side facing the star,” Langton said. “As the atmosphere heats up and expands, it produces very high winds, on the order of 5 kilometers per second, flowing away from the day side toward the night side. The rotation of the planet causes these winds to curl up into large-scale storm systems that gradually die down as the planet cools over the course of its orbit.”
The image above was developed using software from UCSC’s Daniel Kasen, who tuned it to calculate radiative transfer processes that should catch the color and intensity of light this planet produces. Our friend Greg Laughlin, also at UCSC, calls these “…far more realistic than anything that’s been done before for extrasolar planets.” Up next: A possible transit on February 14, which could produce yet more information about this exotic world. Greg’s systemic site will be the place to watch for that.
Have a look at the orbit of this sizzling place in a figure from the paper that Greg just passed along:
Image: Orbital geometry of the HD 80606b system. The small dots show the position of the planet in its orbit at one hour intervals relative to the predicted periastron passage… The size of the parent star HD 80606 is drawn in correct relative scale to the orbit. Credit: Greg Laughlin.
What a place is HD 80606b. According to the paper on this work, the planet receives 828 times more irradiation at perihelion than at the most distant point in its orbit, with a temperature swing from 800 to 1,500 kelvin in a six hour period! The paper is Laughlin et al., “A Direct Observation of Rapid Heating of an Extrasolar Planet,” Nature 457, (29 January 2009), pp. 562-564 (abstract).
by Paul Gilster | Jan 27, 2009 | Asteroid and Comet Deflection |
A small asteroid hitting the Earth’s atmosphere is a spectacular phenomenon, but one likely to go unseen if the object has not been previously tracked. But that may be changing as we continue to install automated cameras across the planet. Take a look at this video of the object that exploded over Scandinavia on January 17. A Swedish camera recorded the event, which now goes worldwide over the Net thanks to the camera’s owner, one Roger Svensson, and spaceweather.com.
The January 17 incident was little more than a lightshow, startling for local wildlife but unnoticed by the sleeping nation beneath the brief glare. It does, however, remind us of the 1017 potentially hazardous asteroids (PHAs) now known to scientists. A PHA is an asteroid larger than 100 meters that may come closer than 0.05 AU to Earth. Prowling around the spaceweather.com site, I find twelve Earth-asteroid encounters this January alone, the closest being the 1.8 lunar distance passage of 2009 BD on January 25. Only one of these is a PHA, a 120-meter rock called 2002 AO11.
A list of close approaches to the Earth by potentially hazardous asteroids can be found here, as assembled by the Minor Planet Center. Necessarily, such lists do not include recently discovered objects whose orbits have yet to be firmed up, and the site points out that the distances involved can be quite uncertain. We’re learning more all the time, prizing out the more unusual of these nearby objects. Below is the MPC’s plot of the inner Solar System. Seen at this scale, the environment the planets move through is a crowded place!
Image (click to enlarge and update): The orbits of the major planets are shown in light blue: the current location of the major planets is indicated by large colored dots. The locations of the minor planets, including numbered and multiple-apparition/long-arc unnumbered objects, are indicated by green circles. Objects with perihelia within 1.3 AU are shown by red circles. Objects observed at more than one opposition are indicated by filled circles, objects seen at only one opposition are indicated by outline circles. The two “clouds” of objects 60° ahead and behind Jupiter (and at or near Jupiter’s distance from the sun) are the Jupiter Trojans, here colored deep blue. Numbered periodic comets are shown as filled light-blue squares. Other comets are shown as unfilled light-blue squares. Credit: Minor Planet Center.
2009 BD is itself a rather interesting object. When it passed by the Earth on Sunday, it was about 645,000 kilometers away, a 10-meter rock whose orbit seems remarkably close to that of the Earth. What this means is that the asteroid will stay around for some months, never wandering further than 0.1 AU until late next year. You may be reminded of asteroid 2003 YN107, which took on a corkscrew motion around the Earth after arriving in our vicinity in 1999. Says Paul Chodas of NASA’s Near Earth Object Program at JPL:
“It’s a very curious object… We believe 2003 YN107 is one of a whole population of near-Earth asteroids that don’t just fly by Earth. They pause and corkscrew in our vicinity for years before moving along.”
The term for these objects is Earth Co-orbital Asteroids, whose population may be augmented by 2009 BD if further study confirms the addition. With an orbit of almost precisely one year, they can catch up with our planet, becoming in effect a small, new moon for the duration of their visit. The co-orbital 2004 GU9, about 200 meters across, has evidently been looping around the Earth for five hundred years. 2003 YN107, on the other hand, has already departed, although it is due for another visit in about sixty years. Needless to say, such objects are interesting targets for robotic or manned exploration.
by Paul Gilster | Jan 26, 2009 | Astrobiology and SETI |
If you’re not a member of the Science Fiction and Fantasy Writers of America (still commonly known as the SFWA from the days before the ‘fantasy’ bit was added), you may not see the group’s regular bulletin. That would be understandable, given that although it can be found on newsstands, the SFWA Bulletin now costs a solid $6.95 per copy. Nonetheless, keeping up with Robert Metzger’s ‘State of the Art’ science column would keep me buying this journal even if it didn’t come as part of my membership.
Metzger, the author of the 2002 novel Picoverse and 2005’s CUSP as well as a variety of short fiction in addition to his science writing (some of which is available online), speculates in his most recent column on a subject we’ve recently treated here. Would a species capable of star travel actually need to make the journey, given the advances in technology that would surely make it possible to learn more and more about exoplanets from its own star system? Metzger reviews current exoplanet work in the context of discovering life from afar, and notes we don’t have to re-do the fabric of spacetime to pull off the trick.
In this era of space-based observatories like CoRoT and (soon) Kepler, most Centauri Dreams readers would likely agree that exoplanetary life may be detected from nearby space (at least with next generation tools), but what gets the attention is Metzger’s riff on how a truly advanced alien culture might view us. No need to land on the White House lawn — why not stay invisible, experiencing our Earth through billions of intelligent ‘motes’ sent by exploration craft the size of dust grains. One mote could dock with every organic entity on the planet, recording everything it experienced and shipping the data back to the home world.
Now that’s telepresence! And yet note Metzger’s next line (italics mine): “As science-fictional as that sounds I would consider such an approach one implemented by a fairly primitive stellar faring race.”
Far more advanced would be the race that could mine the vibrations that occur at the deepest level of our existence. “I’m talking,” writes Metzger, “about what we spew out at the atomic and sub-atomic level, every atom of our body buzzing and spewing, impinging upon the fundamental fabric [of] our reality.” Reconstruct the record that reality imparts in spacetime and this happens:
Out around some distant star, deep in the bowels of some alien mind may sit an infinite number of Earths, each one a snapshot in time, separated by mere pico-seconds, spanning the temporal spectrum from the instant you are reading these words to the moment when the first gravitational perturbation started the coalescence of our solar system out of the thin background of dust and hydrogen.
How would such information be housed and accessed? What uses would alien intelligences make of it? For the answers to those questions, we turn to our science fiction writers, whose job it is to explore such scenarios. Earth may have little to offer a race capable of warping spacetime or skiing through wormholes — not in the physical sense — but as a source of information for study and recreation, we might be just the ticket. The exploration of the galaxy through remote techniques that presume no travel by organic beings has its own logic. Whether the urge to actually be in the places being explored is universal or limited to certain members of a single species remains to be seen. And more than a few science fiction novels might be spun out of answering the question.
