Unfortunately, we can fit only the past year’s top 10 astronomy stories in the pages of Astronomy magazine. Deciding which of the big discoveries from the past year to include was a difficult task. However, we wanted to also showcase the next bunch of important finds from the end of 2010 through the end of 2011. So, here they are in chronological order.
Astronomers find a new moon around Pluto
By Bill Andrews
The Hubble Space Telescope may be best known for its photos of sweeping galaxies and majestic dust clouds, but it’s no slouch on the homefront either. NASA announced July 20, 2011, that the orbiting observatory has imaged a fourth moon, temporarily designated P4, around distant Pluto during a search for rings around the dwarf planet.
Pluto’s other three known moons, Charon, Nix, and Hydra, are all considerably bigger — and thus more easily noticed — than the latest addition: P4 measures some 8 to 21 miles (13 to 34 kilometers) across, while Nix and Hydra each span from 20 to 70 miles (32 to 113 km) and Charon tips the scales at 648 miles (1,400 km). The new moon lies between Nix and Hydra, and P4 completes a trip around icy Pluto every 31 days. (Nix takes 25 days, Hydra 38, and Charon just 6 days to make the same journey.)
“I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles (5 billion km),” says Mark Showalter of the Search for Extraterrestrial Intelligence Institute in Mountain View, California, who led this research.
Astronomers investigate a comet
By Liz Kruesi
On November 4, 2010, scientists got a close-up view of Comet 103P/Hartley. This marked just the fifth time a spacecraft visited a comet nucleus, and the flyby provided such clear images that scientists could link gas and dust emission to specific features on the comet’s surface. NASA says the EPOXI mission’s spacecraft came within 435 miles (700 kilometers) of Hartley.
Images from the flyby revealed this comet contains about 100 times less volume than Comet 9P/Tempel, the other comet this same spacecraft visited. (EPOXI combines two missions: EPOch [Extrasolar Planet Observation and Characterization] and DIXI [Deep Impact eXtended Investigation]. The project uses the Deep Impact spacecraft, which launched a projectile into Comet Tempel in July 2005. EPOXI used the craft’s two imagers and one infrared instrument to investigate Comet Hartley.)
When the spacecraft was about 50 minutes from its closest approach, its autopilot began navigating. “Any command we would send to the spacecraft would take 75 seconds to get there,” says Tim Larson, EPOXI project manager, of JPL. “Not the kind of thing you want to do when you’re talking about hurtling past a 2.2 kilometer-wide [1.37 miles] object at 27,500 mph [about 44,260 km/h].”
As the craft approached, the software determined that the brightest spot in its field of view (aside from the Sun) was the comet nucleus, and thus adjusted the craft’s movement to keep Hartley centered. The comet actually has two bright spots, so the software focused on the most luminous one.
Material escaping from the small “end” and the center appear as one of those bright spots. Scientists determined carbon dioxide jets spew a snowstorm of “fluffy” ice particles at the comet’s ends. “Stereo images reveal there are snowballs in front and behind the nucleus, making it look like a scene in one of those crystal snow globes,” says Pete Schultz of Brown University.
“This is the first time we’ve ever seen individual chunks of ice in the cloud around a comet, or jets definitively powered by carbon dioxide gas,” adds principal investigator Michael A’Hearn of the University of Maryland.
Water vapor escapes through Comet Hartley’s porous material in its much smoother center.
Astronomers will analyze the new data for months. Investigating comets is important because they are “icy rocks” from the early solar system, and so hold information about the formation of our dusty disk.
Saturn and Enceladus connected electrically
By Bill Andrews
Astronomers have found a link between Saturn and one of its most enigmatic moons, Enceladus. A paper in the April 21, 2011, issue of Nature describes an electromagnetic connection between the two that leaves a footprint of light on the ringed planet, which NASA’s Cassini spacecraft detected.
Fans of solar system oddities should already be familiar with Enceladus, whose majestic cryovolcano eruptions spray water vapor far above its south pole. Because Io, Jupiter’s geologically active moon, forms an electrical circuit with its planet, scientists suspected a similar phenomenon could take place with Enceladus. Such a circuit would create a glowing area above the planets’ poles, as energetic electrons following the magnetic field lines constituting the circuit enter the planet’s atmosphere. Jupiter’s poles have these “auroral footprints,” but scientists couldn’t spot any on Saturn — until now. The footprint, visible in ultraviolet light, measures about 750 miles (1,200 kilometers) by 250 miles (400 km) and lies near Saturn’s north pole.
“Scientists started asking if we could see an expected ultraviolet spot at the end of the magnetic field line on Saturn,” says lead author Wayne Pryor of Central Arizona College in Coolidge. “We were delighted to find the glow close to the ‘bull’s-eye’ at the center of our target.”
Predictions of general relativity confirmed
By Liz Kruesi
Scientists launched NASA’s Gravity Probe B in 2004 with the purpose of checking two major predictions of Albert Einstein’s general theory of relativity. After a year of gathering data, and some 5 years of analysis, the satellite has verified those predictions. The findings appeared in the June 3, 2011, issue of Physical Review Letters.
According to general relativity, a gravitational body, like Earth, should warp space and time around it; this is the geodetic effect. The theory also states that a gravitational body will drag surrounding space-time; this is the frame-dragging effect.
For 50 weeks, Gravity Probe B stared at the star IM Pegasi while circling Earth about 400 miles (642 kilometers) above its poles. The spacecraft has four extremely precise gyroscopes. The frame-dragging effect caused their spin axis to shift a fraction of an arcsecond relative to Earth’s rotation, while the geodetic effect caused the gyroscopes’ spin to shift about 6 arcseconds relative to the guide star over the yearlong mission.
Gravity Probe B is one of the longest-running projects in NASA history. The agency first provided funding to research the gyroscopes in 1964. It seems the preparation paid off, as the mission found experimental evidence to back general relativity.
Galaxy survey confirms presence of dark energy
By Bill Andrews
Once again, it looks like Einstein and the elusive concept of dark energy have been vindicated. Two papers published online October 4, 2011, in the Monthly Notices of the Royal Astronomical Society argue that observations from the Australian galaxy survey WiggleZ (pronounced “wiggles”) provide two independent measurements that support the currently prevailing views. “Our new work shows dark energy is real,” says Chris Blake of Swinburne University of Technology in Melbourne, Australia, the lead author of both papers. “Einstein remains untoppled.”
Astronomers learned late last century that the expansion of the universe appears to be speeding up, despite expectations that the gravity from all the universe’s mass would slow it down. To square this conclusion with Einstein’s theories, they had to come up with a mysterious force called “dark energy” to explain what could be powering this accelerating growth.
The original studies examined the brightness of distant stars to learn about the universe’s expansion, but the WiggleZ project looked at two other kinds of data. The first studied the distribution of galaxies, and the second focused on the growth of galaxy clusters and superclusters, both processes where dark energy (or the lack of it) would significantly affect the outcome.
Both tests confirmed the presence of dark energy in the universe, consistent with previous estimates that it makes up about 73 percent of everything (with dark matter and regular matter making up the remainder).
Titan may contain life’s building blocks
By Bill Andrews
The more astronomers learn about Titan, Saturn’s largest moon and one of the most enigmatic objects in the solar system, the more interested biologists become. Scientists at the 42nd meeting of the Division for Planetary Sciences of the American Astronomical Society announced October 7, 2010, that the distant moon’s hazy atmosphere might be capable of producing complex organic molecules.
The international team simulated Titan’s atmosphere in the lab and witnessed the creation of amino acids and the five nucleotide bases necessary for all life on Earth (adenine, cytosine, guanine, thymine, and uracil). While the moon’s surface may be too cold and dark for these reactions to occur, the upper atmosphere’s influx of radiation, sunlight, and other energy likely provides the necessary conditions to create these compounds.
“We don’t need liquid water; we don’t need a surface,” says Sarah Hörst of the University of Arizona, one of the team’s leaders. “We show it is possible to make very complex molecules in the outer parts of an atmosphere.” This shouldn’t imply that life exists on Titan, but simply that these organic materials could form there.
This finding impacts scientists’ understanding of Earth, as well, because it means life on our planet may have begun high in the skies, instead of in a primordial soup, as commonly thought.
Nearest, youngest supernova in a generation found
By Bill Andrews
Astronomers discovered the closest type Ia supernova to Earth in a generation August 24, 2011, and quickly made sure it became one of the best-studied stellar explosions of all time.
The supernova, originally called PTF 11kly and later officially designated SN 2011fe, lies about 21 million light-years away in spiral galaxy M101, located in the Big Dipper asterism of Ursa Major the Great Bear. The Palomar Transient Factory (PTF) survey, which specifically looks for such events in the night sky, discovered the supernova within hours of its birth.
“We caught this supernova earlier than we’ve ever discovered a supernova of this type,” says Andy Howell of the University of California, Santa Cruz, one of the leaders of the discovery team. “On Tuesday, it wasn’t there. Then, on Wednesday, boom!” The PTF’s automated telescopes make it easy to notice tiny differences in huge sections of the sky, letting astronomers know when something changes.
After alerting other observatories to the discovery, astronomers realized the supernova had grown more than 20 times brighter in less than a day. “PTF 11kly is getting brighter by the minute,” says Peter Nugent of the University of California, Berkeley, who first spotted the supernova. Such explosions usually outshine a billion Suns in their first 3 weeks. Their earliest emissions are often too weak to appear in Earth’s skies, but SN 2011fe’s proximity made it easier to see the fireworks from the start.
In fact, it’s so nearby that amateur observers were able to see SN 2011fe with a telescope and even good binoculars. “It is an instant cosmic classic,” Nugent says.
New galaxy smashes distance record
By Bill Andrews
Astronomers probing the data from Hubble’s recent Ultra Deep Field images announced the discovery of what may be the most distant galaxy yet known.
According to a study in the January 27, 2011, Nature, the new galaxy lies some 13.2 billion light-years away, dating from a time only about 480 million years after the Big Bang. “We’re getting back very close to the first galaxies, which we think formed around 200 to 300 million years after the Big Bang,” says co-author Garth Illingworth of the University of California, Santa Cruz.
The finding pushes Hubble’s technology to its limits and still appears as hardly a blip in the space telescope’s images. The galaxy itself seems to be relatively diminutive, measuring hardly 1 percent as large as our own Milky Way. “This result is on the edge of our capabilities, but we spent months doing tests to confirm it, so we now feel pretty confident,” Illingworth says.
To find anything even farther will require Hubble’s successor, the James Webb Space Telescope, and its more advanced optics.
Dawn orbits Vesta
By Richard Talcott
NASA’s Dawn spacecraft entered orbit around Vesta at 12:48 A.M. EDT July 16, 2011, becoming this asteroid’s first known satellite. The capture marked the end of a 1.7-billion-mile (2.8 billion kilo¬meters) journey and the start of a yearlong mission to study this enigmatic world. Vesta ranks as the second-most-massive object in the asteroid belt and the brightest one visible from Earth.
Mission scientists released the first images from orbit August 1. They reveal a world with myriad craters, many of which have intriguing dark streaks on their interior walls. Dawn also captured the first close-up views of the mammoth crater (some 285 miles [460 km] across) that lies near the asteroid’s south pole. Astronomers think many of the Vesta meteorites found on Earth originated in the impact that formed this crater.
Perhaps the most surprising discovery from the initial images is a series of grooves carved into Vesta’s equatorial regions. Each groove is about 6 miles (10 km) wide, and the complete set stretches at least halfway around the asteroid.
Dawn reached its initial science orbit August 11. From an ¬altitude of 1,700 miles (2,700 km), the probe’s camera and spectrometer then started surveying Vesta, resolving objects as small as 820 feet (250 meters) wide.
NASA tours another comet
By Liz Kruesi
The Stardust mission launched in February 1999 to investigate Comet 81P/Wild. The craft flew through that comet’s surrounding cloud of dust and ice in January 2004, and returned a capsule of Comet Wild’s material in January 2006. Shortly after, scientists announced a secondary mission for the spacecraft — called Stardust-NExT (New Exploration of Tempel) — that would fly by Comet 9P/Tempel. After a series of trajectory corrections and also a gravity assist from Earth, the craft reached closest approach to the comet February 14, 2011.
The spacecraft flew by Tempel to image its nucleus and investigate any changes during the past 5.5 years. The Deep Impact mission visited the same comet and sent a probe smashing into it in July 2005. This carved out a small crater on its surface.
Stardust-NExT reached closest approach at 11:39 P.M. EST; at that time, it was 111 miles (178 kilometers) from Comet Tempel. The spacecraft was traveling at a speed relative to the comet of 6.77 miles/second (10.9 km/s).
At 30 minutes prior to closest approach, the spacecraft’s onboard auto navigation system turned on, which helps point the camera. The craft began taking images 4 minutes prior to the flyby, and continued until 4 minutes after. Over those 8 minutes, Stardust-NExT captured 72 high-resolution images of Tempel. (That’s the most the camera can take.) One hour after closest approach, the spacecraft aimed its high-gain antenna to Earth, and about 2 hours later it began uploading the data to researchers.
The camera on Stardust-NExT captures images with a resolution of about 39 feet (12 meters) per pixel. The comet itself is about 4.7 by 3 miles (7.6 by 4.9 km).
Several of the mission’s images show details of the Deep Impact crater. “We see a crater with a small mound in the center, and it appears that some of the ejecta went up and came right back down,” says Pete Schultz of Brown University in Providence, Rhode Island. “This tells us this cometary nucleus is fragile and weak based on how subdued the crater is we see today.”
Stardust-NExT also imaged a side of Comet Tempel that scientists hadn’t seen before. Although the spacecraft is now much farther from the comet, mission scientists will “continue imaging the comet as long as the science team can gain useful information,” says Tim Large, Stardust-NExT project manager at NASA’s Jet Propulsion Laboratory.
A new view of Earth’s magnetosphere
By Liz Kruesi
NASA’s Interstellar Boundary Explorer (IBEX) has had a good few months. Most recently, in mid-December 2010 at the American Geophysical Union meeting in San Francisco, California, scientists on the IBEX team announced that the craft had completed the first compiled image ever of a region within Earth’s magnetosphere called a plasma sheet.
The Sun spews a wind of high-energy particles and gas. Part of Earth’s magnetic field — the magnetosphere — protects us from this material. The solar wind pushes on it, and thus the magnetosphere forms a teardrop shape with a “tail” (called the magnetotail) pointing away from the Sun. Scientists launched IBEX in late 2008 to analyze the magnetosphere and the solar system’s magnetic region (the heliosphere).
The spacecraft studies Earth’s magnetosphere from outside of it — a different view than any previous similar missions. This is how IBEX was able to observe the magnetotail and a surprising denser region called the plasma sheet. Scientists also compared one compiled image with another using data from just a few days prior and noticed fluctuations in the magnetotail.
IBEX doesn’t collect light but instead particles called energetic neutral atoms (ENAs). These form from interactions between the interstellar medium and the solar wind. Because ENAs aren’t charged particles, Earth’s magnetic field doesn’t affect them and they journey unimpeded from where the interactions occur to the IBEX detector.
Astronomers have a few ideas of what causes the fluctuations in brightness within the plasma sheet. One is that the magnetic field lines disconnected and reconnected to produce a denser region of ENAs (which is the red “chunk” of the plasma sheet in the middle image).
Another possibility is that an increase in solar wind pressure could squeeze the magnetotail and heat it up, which would also create more ENAs. Because this was the first time astronomers imaged the plasma sheet, they need further observations to determine what’s causing the brightness changes. IBEX scientists hope to image other variations in the magnetosphere over the next few years.
