A Mundane Cause for the Pioneer Anomaly?

Everybody loves a mystery, and the one surrounding Pioneer has everything going for it, an unusual effect observed via two of the most distant spacecraft ever launched. Both Pioneer 10 and 11 are slowing a bit more than expected as they move through the outer reaches of the Solar System. Explanations range from a variety of on-board causes to suggestions that our understanding of gravity itself needs an upgrade.

NASA’s Slava Turyshev, as noted in this New Scientist story, is compiling data from the spacecraft that had previously been inaccessible due to data formats and media incompatible with modern equipment. Turyshev’s work may take a year to complete, but it holds the promise of nailing what many think to be the probable cause of the anomaly: heat from the RTGs (radioisotope thermoelectric generators) that provide power for the probes. Asymmetrical radiation of that heat just might do the trick.

Meanwhile, New Scientist also gets into far more exotic possibilities, noting that ways of ‘tweaking’ gravity to account for the Pioneer anomaly don’t gibe with the observed orbits of the outer planets:

If you allow violations of [Einstein’s] equivalence principle, modifying the laws of physics can explain the Pioneer anomaly without messing up the orbits of the outer planets, says Robert Sanders of the University of Groningen in the Netherlands.

A theory called modified inertia, proposed by Mordehai Milgrom of the Weizmann Institute of Science in Rehovot, Israel, does just this. It says the way objects accelerate under gravity depends on their past trajectories – a breach of the equivalence principle. In this scenario, the Pioneer spacecraft, whose trajectories are taking them out of the solar system, experience an anomaly, while the outer planets, whose orbits keep them bound to the Sun, do not.

Fascinating stuff, but is there any need to invoke it? The odds on a more mundane explanation are enhanced by Norwegian physicist Kjell Tangen, who leaves the equivalence principle alone and finds no explanation for the Pioneer anomaly in disruptive revisions to the law of gravity. With Turyshev hot on the case, smart money will probably ride on the RTGs for now, but we have no conclusive evidence at this point, so for at least a year the odd journeys of these spacecraft will still inspire controversy.

Exoplanet Announcements at Santorini

Steinn Sigurðsson (Pennsylvania State) has been reporting from the Greek island of Santorini, where he is attending the Extreme Solar Systems conference. I want to send you at once to Steinn’s Dynamics of Cats weblog, where updates are being filed and will presumably continue through today, the conference’s last day. It sounds like a terrific gathering filled with the energizing news of discoveries, its theme being, in addition to finding Earth-like planets, the study of exoplanets in tricky places like dense star clusters, near giant stars and orbiting pulsars.

That last is fitting enough, given that the first extrasolar planets of Earth-like mass were discovered 15 years ago around the pulsar PSR 1257+12; in fact, the conference meets on the occasion of that anniversary and celebrates as well the sixtieth birthday of Alex Wolszczan, the discoverer of those worlds. All of that and beauteous Santorini too, though as Steinn reports, the heat has been the worst since 1916, as per locals who should know.

Steinn has to honor embargos and there are things he can’t speak about, but among the more interesting things to emerge is that the California-Carnegie team has found a true Jupiter analogue around a G8V main sequence dwarf, orbiting at about 4.4 AU. From Steinn’s notes:

This is a Jupiter – a cold gaseous giant planet in the right place, which does not look to have migrated or done anything messy. It is of course a fabulous target for low mass rocky planets interior to the current known giant, including in the habitable zone. It is also a very promising indicator that the large number of known “trending” systems being monitored will resolve out to be solar system analogs – maybe 20-30% of stars being monitored may be solar system like if this all pans out – but that is speculative at this stage.

Some other intriguing notes:

  • Nine nearby white dwarfs are now known to have confirmed warm debris disks;
  • Planets around giant stars seem to be proliferating. The California-Carnegie team has reported three confirmed Jovian planets and four other candidates; the East-Asian Planet Search Network (EAPSNET) likewise has a detection around a K giant in an open cluster and several candidates; and the Pennsylvania State-Poland search team also announces several detections with a whopping thirty candidates.
  • A number of low-mass planet candidates are emerging around K and M stars, but no formal announcements as yet. Take note of Steinn’s provocative comment: “I don’t think the “Rare Earth” hypothesis is holding up well, the pieces of the argument are being dismantled wholesale as we find more systems and gain more understanding.”

And this should interest those interested in the nearest stars, quoting Steinn again:

There is now data on Barnard’s star and Proxima Cen with good velocity sensitivity (~ 3 m/sec). Barnard’s star (old nearby M dwarf) is active and velocity variability correlates with photometric variability – Proxima Cen is very variable, but the fluctuations in velocity do not correlate with the fluctuations in brightness. Maybe something there if the data can be dug into. Should have better than 1 m/sec observations with UVES spectrograph on the VLT telescope. This will get to sensitivity of one earth mass in the “habitable zone” (which isn’t really, the star is variable). Maybe there is a low mass planet in moderately short period orbit around Proxima Cen – be interesting if that turnsout to be the case.

I don’t want to go any further here (we’ll be discussing many of these findings here in days to come), but I do urge you to read through Steinn’s postings as Santorini winds down. There is much of interest — the Swiss group alone has twelve new planets — and the chance to follow a conference from afar at this level of detail is most welcome. A glance at photos of Santorini from the conference site as well as Steinn’s own snapshots has me thinking about how to get there myself one day soon.

The Latest Carnivals of Science

The 11th edition of the monthly science carnival Philosophia Naturalis is now up at Chris Rowan’s Highly Allochthonous site, where discussions move from the Higgs boson to Cassini’s extended mission, with time in between to investigate puddles on Mars. Take note as well of the weekly Carnival of Space, now in its 9th edition, this week edited on the Planetary Society’s weblog by the able Emily Lakdawalla. Here again the range is spacious, with musings on the atmospheres of extrasolar planets to the nano-minded Brian Wang’s thoughts on laser systems that could get us to Mars. If you only have time for one, don’t miss Pamela Gay’s take on gravitational lenses, a fine job on a tool of ever growing importance.

Asteroid Watch: Saving Arecibo’s Radar

“Let’s hope that we find all the dangerous asteroids in the next few months,” says Cornell astronomer Joseph Burns. He’s talking about the Arecibo Observatory in Puerto Rico, which Cornell manages for the National Science Foundation. Word is that Arecibo’s radar system may lose its NSF funding as early as 2008, leaving us without our premier tool for tracking asteroids of the Earth-crossing variety.

The Arecibo Observatory

Strictly speaking, Cornell’s Arecibo effort runs through the university’s National Astronomy and Ionosphere Center (NAIC), which will need to find outside partners to pick up as much as half of the observatory’s operating costs or face the threat of total shutdown of the Arecibo telescope by 2011.

Image: Aerial view of the Arecibo Telescope, equipped with a 12.6cm, 1.0MW radar transmitter. Credit: NAIC/Cornell University.

It’s hard to understand why, in its deliberations on the matter, the NSF all but ignored the contribution of Arecibo’s radar. In fact, as this Cornell news release makes clear, not a single planetary scientist had a presence on the relevant committee, nor did the term ‘asteroid’ make an appearance in its report. The response from some astronomers has been unambiguous, as in this statement by Cornell’s Jean-Luc Margot:

“Asteroid impacts are the only known natural disaster that can cause ecological disaster and mass extinction. They can be prevented, though, and it is simply irresponsible to neglect a unique warning and mitigation device like the Arecibo radar.”

The key date appears to be September 30, 2008. Absent new funding from NASA, NSF or outside sources, that’s the day Arecibo’s radar will likely be deactivated. $1 million a year is needed to cover operating costs, a bargain in the eyes of some, who point not only to the radar’s capabilities at asteroid tracking, but also its contributions to science, including the discovery of ice at Mercury’s poles and detection of the so-called YORP (Yarkovsky-O’Keefe-Radzievskii-Paddack) effect, which can change the rotation rate of an asteroid.

Do we give up on Arecibo? The Goldstone radar system in California is twenty times less sensitive, not an adequate fallback for planetary science or asteroid tracking. Perhaps NSF will reconsider, heeding the urgings of the chair of the American Astronomical Society’s Division for Planetary Sciences and other astronomers. But this is a classic case for alternate sources, and we’ll watch any attempts to fund Arecibo through the private sector with great interest.

Related: In a request for a Congressional hearing on near-Earth objects (NEOs), Rep. Dana Rohrabacher (R-CA) notes NASA’s March 2007 report “Near Earth Object Survey and Deflection Analysis of Alternatives.” NASA predicts 20,000 objects with the potential energy of 100 megatons of TNT or more that can be considered dangerous to Earth. The Spaceguard program currently aims to detect 90 percent of NEOs with a 75,000 megaton potential. If successful, this program would probably find only 35 percent of the 100 megaton objects. A 100 megaton collision, says Rohrabacher, is predicted to cause a minimum of 50,000 fatalities.

DNA as Cosmic Code

If you possessed technologies so advanced that you could seed life throughout the cosmos, wouldn’t you leave some marker that would identify your work? We can’t know what a hypothetical extraterrestrial intelligence might do, but we do know enough about human nature to acknowledge the desire for recognition. It shows up every time a new squabble breaks out over who really discovered an exoplanet — humans crave the praise of their fellows. Yes, if humans had life-seeding technologies, you can bet we would leave signs of our craftsmanship.

Consider what the Keio University team working under Masaru Tomito has done in Japan. As explained in a New York Times essay by Dennis Overbye, they’ve inserted copies of the immortal equation E=mc2, along with the date of its derivation (1905) into the genome of a bacterium. Thus we see DNA as a kind of archival medium. Overbye is reminded of Jaron Lanier and David Sulzer’s idea of encoding a year’s worth of the New York Times magazine into the ‘junk’ DNA of a cockroach, the one creature likely to survive even the worst potential disaster including nuclear holocaust. Says Overbye:

If cockroaches can be archives, why not us? The human genome, for example, consists of some 2.9 billion of those letters — the equivalent of about 750 megabytes of data — but only about 3 percent of it goes into composing the 22,000 or so genes that make us what we are.

The remaining 97 percent, so-called junk DNA, looks like gibberish. It’s the dark matter of inner space. We don’t know what it is saying to or about us, but within that sea of megabytes there is plenty of room for the imagination to roam, for trademark labels and much more. The King James Bible, to pick one obvious example, only amounts to about five megabytes.

Leading to the speculation that our own genome may contain some kind of information, assuming that the early Earth was scattered with DNA delivered by an alien species for the purpose of propagating life. But DNA’s mutability reduces the chance that a single ‘message’ might survive. This is why the Japanese researchers added redundant copies of E=mc2 into the bacterial genome, allowing Einstein’s equation to have a chance. Presumably ancient bio-engineers would have done the same.

And I like the way Overbye puts the matter:

The challenge for an erstwhile interstellar Johnny Appleseed is to make the message part of the basic nature of its host.

If that ever turns out to be us, if we find that we are the medium, to paraphrase the late Marshall McLuhan, then, in some sense, we are also the message. Never mind who or what are the intended readers.

Ponder, too, what the implications would be if we really did turn out to be derived from primordial DNA developed just for the purpose by a species we might one day encounter (or, more likely, its descendants). Would we expect to find something like the DNA we’re familiar with on Earth no matter where we went in the cosmos? Allowing the possibility of intelligent species arising billions of years ago, would we expect any trace of the ancient planet-seeding race to remain?

And if there were a message tucked into the vast recesses of our DNA, a message that had somehow survived, what would it be? The key to a further breakthrough in intelligence or technology? Perhaps. But I’m reminded of the glorious stained glass that adorns the cathedrals of Europe. As they went about their work, the artisans who produced these many-hued wonders often inserted real faces into their scenes. King David in the image might bear the likeness of the local baker. Mary Magdalene would suggest the mayor’s wife. Often the artist inserted his own visage somewhere in the picture, a way or surviving, if only in a shaft of patterned sunlight, the world all artists knew to be transient.

Who knows, maybe there’s a face in the stained glass of our DNA. Be sure to read the Overbye essay. He’s a terrific writer — he could hold my attention if we were writing about wallpaper paste. His Lonely Hearts of the Cosmos: The Story of the Scientific Quest for the Secret of the Universe (Harper Collins, 1991) is one of the great tours de force of modern science writing, at once approachable, elegant and impeccably researched. Needless to say, I have the Times‘ science feed set up in my RSS reader so as not to miss any of Overbye’s work.