James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 42nd Annual GLPA Conference, Merrillville, IN, October 25-28, 2006, reprinted by permission.


This Update could be called the "year of the planets." The advances in our knowledge of Mars, Saturn, asteroid/comets, the Kuiper Belt, and of exoplanets orbiting other stars were so great that they could only be sampled. We might say the same for neutron stars and pulsars, as the more we look the less we seem to understand, the seeming "nutty" ones perhaps being the more common. And then there is Pluto...

Birth, Death, and Continuation

Begin with events close to us. Too bad "Hubble" rhymes with "trouble": the phrase is way overused, though certainly apt. This amazing instrument, which has survived now for over 16 years (though not as long as this Update series), is truly in difficulty with failing instruments and control gyros, NASA, however, seems to have overcome its seeming inability to fix it. Repair is now on the way!

SOPHIA (Stratospheric Observatory "PHor" Infrared Astronomy) is suffering from a similar level of schizophrenia. This 2.5 meter telescope, which is designed to examine the infrared sky from over 40,000 feet from the side of a converted Boeing 747, was -- after years of design and construction -- canceled because of NASA's budget priorities. Then suddenly it was back on the books again, though delayed by the FAA (who oddly seems to have trouble with a huge hole in the side of a jetliner...)

Passed away was Princeton's John Bahcall, who was "instrumental" in getting us the Hubble Space Telescope and who delved deeply into the Sun and the now-solved neutrino problem. Passing in one way or another is the Yerkes Observatory, which has run its course as a research institution, and which the U of Chicago is trying to sell to a developer with the Observatory proper kept as an educational institution, the whole story yet to unfold.

At the other end of life, CARMA (Combined Array for Research in Millimeter-wave Astronomy) was born in California by combining the BIMA (Berkeley-Illinois-Maryland Association) millimeter array with the OVRO (Owens Valley Radio Observatory) at a new, high, dry site. Its six 10-m and nine 6-m radio telescopes make the world's top millimeter array. In the middle, we salute the Sloan Digital Survey, which has been extended to 2008 to map the Galaxy.

The Sun

Also in the middle, of both the Solar System and of its 10- billion year lifetime, is our Sun, which we -- addicted to it as we are -- are desperately trying to understand. The current sunspot cycle will bottom out in February of 2007, while the new one has already begun. At peak, the Sun throws out several coronal mass ejections a day. A big one can ionize the upper atmosphere and thus mess up radio signals to the point where GPS satellite positions can be tens of meters wrong (leading you to the road to Keokuk rather than to Kalamazoo). In addition to the remarkable SOHO (SOlar and Heliospheric Observatory) satellite, we will now have the just-launched STEREO (Solar TErrestrial RElations Observatory) twin solar satellite, which will be able to image the Sun and its ejections in three dimensions.

And Actually Some Stuff About the Moon

We have long realized that the upland cratering came from an ancient "heavy bombardment" of debris that took place not long after the Solar System was born. Now we see that the distribution of crater sizes nicely fits the distribution of asteroid dimensions, confirming where the impactors came from.

First the Inner Planets

Akin to the collisional formation of the Moon by a large Mars- size body hitting primitive Earth, Mercury is thought to have suffered a collision that stripped off much of its outer mantle, leaving it with a relatively huge iron core. The impact would have sent a vast amount of debris outward. Swept up by us, it could have contributed as much as a millionth of the mass of Earth.

A bit farther out, Venus is now the subject of scrutiny by the Venus Express, which went into orbit last April 11 and which carries both visual and infrared imagers. A shot of the south pole shows a huge rotating vortex (oddly similar to the one recently found at Saturn's south pole).

Venus is hot because of its carbon dioxide atmosphere. We seem to be trying to replicate some of that on Earth. It's melting. Well, its glaciers are at least, some withdrawing at an alarming pace.

And what can one say about Mars? It needs its own book. All we can do is pick and choose a topic or two. The Rovers (Spirit and Opportunity) claim top prize. Designed for three Martian months, they have each outlived their expectations by a factor of 10. Spirit has travelled over four miles, while its brother is approaching six! So if there is water, which everything leads towards, where are the carbonates? Very acidic water, indicated by sulfates, may have stopped their formation. MARSIS radar of ESA's Mars Express then shows one to two kilometers of ice under the layered deposits at the poles, with more ice extending down to 60 degrees latitude.

Followed as Usual by the Outer Planets

Jupiter's Great Red Spot (so-called because it is big, sort of red, and clearly a "spot") has been spinning around for more than 300 years. It was joined by a rather cute "Red Spot Junior," which differential rotation (really shearing winds) has brought ever closer to the Big One, which will probably absorb it.

And, as in the case of Mars, another book can (and will) be written about Cassini's Saturn. Picking and choosing, we have a new rotation period of 10 hours 39 minutes and 22 seconds, not far off the old one. We also see tiny moons in the rings that suggest that the rings are the result of a collisional breakup of an icy satellite. The real show is the amazingly diverse set of larger satellites. There is no way to summarize them all. Choose three. Hyperion, which tumbles chaotically, has a density of just 0.6 grams/cubic centimeter, is icy, and may be a captured comet nucleus. Enceladus sports water geysers at its south pole. The heat may come from energetic particles in Saturn's magnetosphere.

The show's star is Titan. The 1.5 bar atmosphere (at the surface, where the temperature is just 93 Kelvin) is dynamic. We see lightning as well as direct-rotation winds of 430 kilometers per hour 120 kilometers up that switch to retrograde near the ground. Dry lakes, shorelines, tributary systems tell of running/standing methane. Though now unfilled, a cycle of some sort probably brings fierce occasional methane rains. Nitrogen isotope ratios then tell of a much thicker air blanket in times gone by.

While in bulk very different from Jupiter and Saturn (having much more heavy stuff within them, water and the like), Uranus and Neptune also share the possession of ring systems. Two more have been found around Uranus, both farther out than the originals. As opposed to the dark inner rings, the outer new one is blue. While the first Kuiper Belt Object (KBO) known is usually considered to be (dare we speak the name) Pluto, the honor really goes to Triton. Neptune's largest satellite, a near-clone of Pluto, orbits backward, suggesting capture. The latest theory is that when free, Triton had a companion. Coming too close to Neptune, the companion was ripped away, while Triton was slowed and caught in the retrograde orbit. At the same time, it wiped out most of Neptune's natural moons.

The "Rest of It All" makes for a very long section. So we'll break it up.


Meteorites are just asteroids that hit the Earth. Some are common stones, others rarer irons. Among the rarest, and perhaps most beautiful of all, are the stony-metal pallasites (NOT from Pallas!) from the core-mantle boundary of a busted asteroid. A record 635 kilo monster was found buried in Kansas. I doubt it will lower their price.

Ceres, the biggest of the asteroids, has been found by Hubble to measure 975 X 909 km, which gives a mean density just 2.1 times that of water. The shape, rotation rate, and smoothness point to a rocky core and icy mantle (with more fresh water than found on Earth). One wonders which asteroids differentiated and broke up to create the iron meteorites.

Such breakups also produce fine grains that find their way to Earth and produce dust showers, as did a collision that created the current asteroid 409 Veritas and its family some 8.3 million years ago. We truly are of the cosmos!

Then there is poor Hyabusa, the Japanese spacecraft that attempted to put a lander on, and bring home dust from, asteroid Itakawa. While the main mission seems to have failed, the probe did provide some marvelous images, including one of its own shadow against the bright reflective asteroidal surface. The smooth natures of such asteroids are apparently the result of violently vibration from impacts.


More comets are seen masquerading as main belt asteroids, their true natures revealed by tails. Similarly, a binary pair found among Jupiter's famed Trojan asteroids (which orbit in wide packs 60 degrees ahead of and behind the planet at stable "Lagrangian points") have such low densities (from orbital analysis) that they may well be Kuiper Belt comet nuclei that have been moved inward by planetary perturbations and then trapped. While two is a pretty small sample, perhaps all the Trojans are such.

On the other hand, "StarDust" was a "Wild" Success, visiting Comet Wild 2 (pronounced "vild" with a short "i") and capturing the comet's dust for successful return to Earth. We see the surprising inclusion of olivine and other materials with high melting temperatures that should not be in comets created in the deep freeze of the outer solar system. Anyone interested can join the group to search for the microscopic dust tracks within the trapping medium.

Then Deep Impact, which sent a deliberate hit onto Comet 9P/Tempel, showed it to be a rubble pile with a very low density of 0.6 that of water, which in turn shows that much of it IS water (ice). We also find carbon dioxide, hydrogen and methyl cyanides, various organics, again olivine, carbonates, and clays (and thus we are back to water). Ice seems to cover some one percent of the surface.

All comets that invade the inner solar system are doomed, as seen by the amazing breakup of Schwassmann-Wachmann 3. Since comets keep coming in to us some five billion years after the Solar System was formed, there must be huge reservoirs of them, one of which is the above Kuiper Belt, one of which is, and here we go, PLUTO.

Pluto and the KBOs

Not an 80s band, but a controversy, one that has brought astronomy into the public eye, but not always very flatteringly (if that is indeed a word). Pluto, our "ninth planet," has long been known to have a wacky orbit, the planet going between 30 AU (inside that of Neptune) out to 50, with a high inclination that can take it well out of the Zodiac. It has also been captured by Neptune in a 2:3 resonant orbit, Pluto making two orbits for Neptune's three. So Neptune has TWO of the critters, the other its moon Triton (as above). We now recognize over 1000 objects that inhabit the Kuiper Belt reservoir, which seems to extend roughly to 55-60 AU from the Sun, many sharing Pluto's 2:3 resonance. Pluto clearly belongs. As does a slightly bigger KBO, 2003 UB313 (from Hubble, 2397 km diameter, 2380 for Pluto). Now an amazing 96.6 AU from the Sun, it shines at magnitude 19, far below Pluto. But it too also comes inside Neptune's orbit, 37.7 AU, even closer than Pluto. Had it been closer to us and found in 1930 along with Pluto, it would have been the tenth planet. So is it (and a variety of other KBOs a bit smaller than Pluto) also a "planet," giving us more of them than anyone wishes to memorize? Or do we, as the International Astronomical Union says, put Pluto to pasture? Apparently so. Accordingly, the IAU then gave 2003 UB313 the name Eris (Greek goddess of discord) and her Moon (half Eris's size, making the system even more like Pluto) the name Dysnomia (goddess of lawlessness). We'll probably find more big KBOs. But culturally, Pluto is, and will probably remain, a "planet." In view of the age of discovery, how about "Honorary Planet"?

In other KBO news, "Buffy" has a circular orbit with a crazy 47 degree tilt, while 2003 EL61 spins fast and may have one axis even bigger than Eris. Then we watch the X-ray source Scorpius X-1 (which lies nicely in the Zodiac), and see what appear to be occultations by 100-meter-wide KBOs. What wonders we are uncovering as we expose more and more of the Solar System's inventory. Which all came from out there, from the collapse of especially dense, rotating interstellar clouds.

Interstellar Stuff

The past year has seen some spectacular new imaging, presented here as topics come up. Among the most remarkable is the gigapixel image of the Orion Nebula (for which there is a download warning). At the heart of the Nebula is the set of Trapezium stars that were born from a cosmic cloud and now illuminate their surroundings. Infrared imaging revels the Trapezium to be at the heart of a vast cluster less than a million years old.

Got Deuterium? We do now. The Galaxy has long been mapped with the famed 21-cm line of neutral hydrogen (caused by hydrogen's electron reversing its spin direction from the same as the proton's to the lower-energy reverse). Now we finally have the analogous 92 cm line of deuterium, which allows an interstellar abundance of 0.000025 relative to normal H, right on the prediction from the WMAP cosmic background observations (more WMAP results below).

Other Planets

Here we are back in Mars/Saturn territory. There is SO much new, that one can only pick and choose so as to get the sense of discovery. As of the moment, there are 210 known exoplanets (those orbiting other stars), that include 20 multiplanet systems. Mu Arae is the champion with four orbiters. The Doppler technique (precision down to 1 m/s) still leads the way, but observations of planetary transits are also paying off. Hubble, for example, sampled 180,000 stars in their SWEEPS field, and found 16 candidates. On occasion we can do both, which really nails down planetary properties. Observation of circumstellar disks and astrometric observations (positional shifts) add to the mix. A sample of discovery, famous stars first: Planets also seem to form nicely -- perhaps even better -- in binary systems (note 16 Cygni). Wouldn't it be neat to be able to visit another star and its planetary system? Dusty disks around brown dwarfs (substars below the 0.075 solar-mass fusion limit) suggest that they too can harbor planetary systems, while dusty circumstellar matter around white dwarfs suggest destroyed systems.

Brown Dwarfs

Hard to believe that just a few years ago we saw none at all. Now we estimate that the Galaxy may contain 100 billion of them, a third the total number of regular stars. Thanks to an eclipsing pair of them, we now have more brown dwarf masses: 56 and 36 times that of Jupiter, clearly below the 80 Jupiter-mass fusion limit. Oddly, the more massive is the cooler, opposite that expected, showing how confusing these small bodies really are. Brown dwarfs are so cool that they can even precipitate solid-grain "clouds" that further confuse our analyses. Another binary (wide, no orbit) yields record low-mass estimates of 17 and 15 Jupiters (and perhaps as low as 14 and 7, carrying one down below even the deuterium-fusion limit of 13). Do brown dwarfs overlap planets? Can planets be made in different ways, both "bottom-up" from accumulation of dust and "top down" by direct condensation? The problem makes that of Pluto and the KBOs look simple.

Real Stars, Some Quite Famed

Does Proxima Centauri, the closest star, really belong to Alpha (which is itself double)? Astrometry from Hipparcos says YES, that the system is just barely bound together. Polaris is not only double (the well-known companion a class F dwarf 18 arcseconds away), but triple with a much closer F dwarf 0.2 seconds of arc distant. Polaris is the brightest Cepheid, not that you can see the variations (as you can for Delta Cephei); they are only a couple hundredths of a magnitude as the star switches from the first pulsational overtone to the fundamental (or so we think). Cepheids, including both Polaris and Delta Cephei, are found to lie within large circumstellar clouds of dust (as indicated by IR observations). For fame, it's hard to top Vega, which has always seemed too bright for its class (A0). Seemingly a slow rotator, Vega is now known to be a rapid rotator (12.4 hour period) seen pole-on, and like other spinners (Fomalhaut, Altair) is quite oblate. It is thus subject to "gravity darkening," in which the pole (closer to the center) is hotter and has a greater surface brightness than the equator. We can now take such variations into account in the models for better abundance analysis.

Red dwarfs have fewer binary systems than sunlike stars, making fewer than half the stars actually double. At the other organizational end, we are surprised to see that our Galaxy is still forming massive clusters. The 2MASS (Two Micron All Sky Survey) project finds one of 20,000 solar masses with 14 red supergiants, each of which will probably explode. And all nearly at the same time (astronomically speaking of course).

Lower mass red giants lose their outer envelopes. Exposing their old nuclear-burning cores, they become white dwarfs. In the transition, at least some of them create planetary nebulae (PN), in which the hot stars light up the fleeing envelopes. While giant-star mass loss is spherically symmetrical, PN commonly have bizarre, bipolar shapes. A magnetic field in water-rich flows from a developing PN suggests that such fields do the shaping work. Other PN may be influenced more by binary action. In fact, some think that it takes a binary to make a PN in the first place.

And speaking of PN, be sure to note the amazing image of the Helix (NGC 7293) taken by Spitzer.

A nova is produced by the overflow of matter from an ordinary (sunlike or below) dwarf onto a very close white dwarf companion. When the infalling matter compresses and heats, the fresh hydrogen-rich surface layer blows up in a natural hydrogen bomb (carbon-cycle) explosion. The white dwarf survives and repeats its action every hundred thousand years or so. If the white dwarf is very massive, though, the repeat cycle is much shorter. RS Ophiuchi, a "recurrent nova," did it again in 2006 (as it did in 1898, 1933, 1958, 1967, and 1985). The white dwarf is believed to increase its mass with each cycle, such that RS Oph and its kin may push their white dwarfs past the 1.4 solar mass Chandrasekhar limit to create Type Ia supernovae (the prime standard candles in the cosmology business).

At the massive stellar end lies Eta Carinae, at some 6 million solar luminosities one of the Galaxy's brightest stars. The evidence continues to pile up that it too is really binary with a 5.54 year period (this year the clue is the eclipse of the companion's ultraviolet light by the more massive star's wind). The companion, probably a stripped Wolf-Rayet star, used to be the more massive of the pair, and will most likely be the first of them to "go supernova" via core collapse (Type II). Speaking of which:

Supernovae, Pulsars, and Black Holes

The Very Large Array finds an amazing number (35) of newly known supernova remnants in the inner Galaxy. Supernovae produce radioactive aluminum-26. The amount, determined by X-ray observations, suggests a supernova rate of 1-3 per century, about what was thought. While contemplating supernova remnants, check out the new Hubble mosaic of the Crab Nebula.

The exact mechanism by which core-collapse supernovae actually blow off their outer layers remains a mystery. The collapse to a tiny neutron star from an Earth-sized iron core starts a rebound shock that stalls. Neutrino absorption may then re-start the shock, but that is unclear. We might also invoke powerful off- center acoustic waves, which gives the new neutron star -- or maybe pulsar -- a high-speed kick. We thought we understood pulsars, rotating, beaming neutron stars. Look, though, at some interesting (if not nutty) ones:

Gamma Ray Bursts

About once a day a gamma ray telescope would see a sudden burst from the cosmos, one unconnected with our own Galaxy. There are two kinds, fast and slow, separated at about two seconds. Five short ones from nearby galaxies confirm the notion that they are caused by neutron star mergers. Ones from M 81 and M 82 suggest that some short bursts are actually Soft Gamma Ray Repeaters, which pound out huge blasts of energy from starquaking magnetars (a few of which are seen in our own Galaxy). Long bursts seem to be from ultradistant beamed "hypernovae" from very massive stars. All these, and normal stars as well, are contained in:

Our Galaxy

As we assemble the pieces, we can get better and better ideas of the structure of the system in which we live. Our Milky Way Galaxy is clearly a barred spiral. Our core, the Galactic nucleus, has been resolved, Sagittarius A* (as it is called) about 1 AU across. With a measured mass between two and three million times that of the Sun, it almost has to be a supermassive black hole.


Like ours, the Andromeda Galaxy, M 31, seems to be barred, the true nature long-hidden by the severe tilt to our line of sight. An eclipsing binary within M 31 gives another measure of distance, 2.52 million light years, which agrees perfectly with that derived from Cepheid variables. M 31 seems to have a hole in it, made when M 32 barged its way through, again showing the propensity of galaxies to collide. It more and more seems that galaxies suffer periodic collisions, and that big ones are built from the mergers of smaller ones, mergers that help create and feed central supermassive black holes.

Yet here and there we still find unexplained oddballs, to wit, a galaxy with half a billion solar masses of neutral hydrogen but almost no stars, seemingly in a primitive state. Are there more?


Quasars are the ultraluminous central black holes (made bright by surrounding infalling gas) of ancient, distant galaxies (our own nucleus sort of a nearly-dead quasar). Now Hubble has found a "naked quasar," with no surrounding galaxy. We once thought they were all naked. A deeper exposure will most likely reveal it.

Galaxy Clusters

Ages ago, we examined the orientations of stellar rotation axes in our Galaxy to see if they align somehow with the disk. They don't. Yet, curiously, the disks of spiral galaxies actually seem to align at right angles with the large-scale filaments and walls of galaxies in which they reside.

And Finally, Everything

We get an analysis of the origin and current state of the Universe through a variety of observations that include the expansion (through Type Ia supernovae), observation of galaxy clusters, and the ripples in the Cosmic Microwave Background (the CMB), the cooled radio-remnant of the Big Bang. Current data give an age to the Universe of 13.7 billion years, and that it is made up of 4 percent baryons (protons/neutrons), 22 percent dark matter, and 74 percent dark energy (the mass equivalent thereof). Polarization of the CMB from the WMAP (Wilkinson Microwave Anisotropy Probe) supports previous conclusions. At the release of the CMB the Universe went "dark. The polarization then gives a time for "re-ionization" by the first stars of 400 million years after the Big Bang.

On the negative side, Type Ia supernovae may not really be all the same; their natures may depend on galaxy type. (The two theories for formation involve the overflow of a white dwarf from a tidally disturbed companion and a binary white dwarf merger.) Then there is the very distant galaxy that appears to be only a 500 million years old, showing galaxies to have formed anomalously fast as compared with expectations.

At the end, we see many successes. But the deeper we look there are also increasing mysteries. How did the Big Bang even come to be? Were there multiple ones, are there other universes? We don't know. But we do know that ours, the one we inhabit, led directly to us, to our own world, to our own hearts, minds, and butterflies.
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