ASTRONOMY UPDATE 2006
James B. Kaler
Department of Astronomy, University of
First published in the Proceedings of the 42nd Annual GLPA
Conference, Merrillville, IN, October 25-28, 2006, reprinted by
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
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
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
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
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
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
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
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 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.
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).
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
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
- Beta Pictoris not only leads in the disk department, but has
a second, smaller tilted disk that suggests the gravitational
effect of an unseen orbiting planet.
- Pollux has a planet at least 2.9 Jupiter masses in a 590 day
period with an orbital radius 1.69 AU, making it the first
confirmed giant with such a companion.
- Epsilon Eridani's planet is now confirmed astrometrically by
Hubble. This closest of extrasolar planets has a mass 1.5 times
that of Jupiter, and orbits in 6.9 years at a mean distance of
- Doppler observations of HD 189733 coupled with a transit give
a planetary mass of 1.15 Jupiters, a radius 1.26 times that of
Jupiter, and (from infrared detection) a temperature of 844 C.
- Infrared observations by the Spitzer Space Telescope reveal
the day-night temperature variations of one of Upsilon
- Gravitational lensing of a distant star suggests a planet
only 5.5 times more massive than Earth.
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
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
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:
- New speed record for hustling pulsar of 1000 km/s, which
could take it clean out of the Galaxy.
- A millisecond pulsar in a binary with a white dwarf weighs in
at 2.1 Suns, perilously close to the neutron star limit (which
may be up to 3 solar).
- Now we get RRATS, "Rotating Radio Transients," which beam
millisecond bursts that at the instant of release are the
brightest radio sources in the sky. Observed periodicities of
seconds imply neutron stars. They may far outnumber "normal"
- Another has a 0.6 second period for a week or so, and then
turns off for a month.
- Finally (at least for this list) is the slooowwwww pulsar,
with a 6.7 HOUR period. The braking mechanism is not at all
clear. It may be one of the rare magnetars with fields 100 to
1000 times "normal" (over 10**14 times that of Earth).
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:
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
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.
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
See main page for copyright