To date, we have discovered 865 confirmed exoplanets orbiting distant stars. But a great mystery remains: how do these planets form?

Theories on planet formation seem to fall apart when astronomers run simulations based on the laws of physics. Computer models show that clumps of dust orbiting around a star would either become large enough to smash into other clumps then break apart, or drift too close to their parent star then break apart. Either way, the clumps of matter do not survive long enough to form anything as large as a planet. When theories fail, observations often come in handy, to help scientists refine their theories with better data.

Enter the Atacama Large Millmeter/Submillimeter Array (ALMA), which only recently started making observations but has already sharpened our view of distant astronomical objects.

When it imaged a region around a particular young star in the constellation of Ophiuchus, ALMA observed a cashew-shaped dust cloud rather than the expected dust ring. This unusual structure could possibly trap large dust grains, keeping them safe during the beginning stages of their development. Scientists have affectionately described the formation as a “dust trap.”

Nienke van der Marel, a PhD student at Leiden Observatory in the Netherlands, explains, “It’s likely that we are looking at a kind of comet factory as the conditions are right for the particles to grow from millimeter to comet size. The dust is not likely to form full-sized planets at this distance from the star. But in the near future ALMA will be able to observe dust traps closer to their parent stars, where the same mechanisms are at work. Such dust traps really would be the cradles for new-born planets.”

The researchers think that larger dust particles could grow in the dust trap long enough to form a planet’s core. While growing within the dust trap, the planetary seed would be protected from factors that could inhibit its growth.

“Trapping the large dust particles prevents the radial inward drift and therefore allows the particles to grow to much larger sizes, up to rocks as wide as a kilometer or more,” Van der Marel adds. “The existence of dust traps in disks around young stars provides a crucial step in the start of planet formation by dust coagulation.”

This observation provides a crucial step in understanding how planets are formed, although it raises new questions about how dust traps are created in the first place. And so it goes: scientific mysteries often lead to more questions, followed by new theories and new observations.

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA

The scientists used data from NASA’s Cassini, Galileo and New Horizons missions (dating from 1996 to 2009) to search the ring systems of Jupiter and Saturn for patterns of cometary disruptions.

In the case of Jupiter, the ripple-producing culprit was the well-known comet Shoemaker-Levy 9, whose debris cloud hurtled through the thin Jupiter ring system during a kamikaze course into the planet in July 1994. Scientists attribute Saturn’s ripples to a similar object—likely another cloud of comet debris—plunging through the inner rings in the second half of 1983. The researchers believe this comet passed through when Saturn was on the other side of the Sun from Earth.

“We now know that collisions into the rings are very common—a few times per decade for Jupiter and a few times per century for Saturn,” said Mark Showalter of SETI and lead author of the paper on Jupiter. “Now scientists know that the rings record these impacts like grooves in a vinyl record, and we can play back their history later.”

The tightness of the rings’ “grooves” gives clues to when the comet debris came hurling through, according to Nature News:

As time passed, this tilt has become a progressively tighter spiral, meaning that the shorter the ripple’s wavelength, the longer ago it was formed.

(Discover has a great NASA video of the rings becoming tighter with age on their site.)

The ripples also give scientists a measurement of the size of the clouds of cometary debris that hit the rings. In each of these cases, the nuclei of the comets were a few kilometers wide before they likely broke apart.

“Finding these fingerprints still in the rings is amazing and helps us better understand impact processes in our solar system,” said Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cassini’s long sojourn around Saturn has helped us tease out subtle clues that tell us about the history of our origins.”

“What’s cool is we’re finding evidence that a planet’s rings can be affected by specific, traceable events that happened in the last 30 years, rather than a hundred million years ago,” said Matthew Hedman, of Cornell and lead author of the Saturn paper. “The solar system is a much more dynamic place than we gave it credit for.”

Image credit: NASA/JPL-Caltech/SETI

What do the invention of farming, the fall of the Roman Empire, and the Black Death all have in common? Besides the fact that each represents a turning point in the history of human civilization, new research gives substantial proof to the notion that each was influenced by the weather.

In a paper published this month in Science Express, an international team of scientists used a combination of tree rings and ancient manuscripts to see if the environment may have paved the way for some civilization’s greatest successes, and some of our greatest failures.

The idea that human history has been influenced by changes in climate is nothing new. In 2005, scientist and bestselling author Jared Diamond explored this idea in his book, Collapse: How Societies Choose to Fail or Succeed. Yet despite the work by Diamond and others, high-resolution data analysis that can give us a clear picture of ancient climate patterns, and how they correlate with moments in history, has been limited.

There are plenty of historical sources that give us accounts of ancient and medieval weather patterns. But these reports can be conflicting and contradictory. There is also a wealth of tree ring data used to develop a chronology of Central Europe over the past several thousand years. But no one had thought to compare the two.

The study of tree rings, called dendrochronology, is based on the fact that trees grow in width each year. In good times, the tree will grow a lot, leaving a wide growth pattern called a tree ring. In bad times, it will grow less, leaving a narrow ring. The paper’s authors collected tree ring data for the last 2,500 years from several areas in western and central Europe. The tree ring data was so precise that they could estimate everything from annual rainfall to patterns of deforestation.

The authors then compared the tree ring data to historical written records from the past few thousand years. They found that the patterns of tree deforestation in central Europe lined up perfectly with the arrival of the Roman Empire (and its system of roads), between 300 BC and AD 200. But data from just a few decades later, between AD 250 and AD 500, showed a long period of climate instability. This instability was followed by extreme political and economic turmoil, including the fall of the Roman Empire.

The team found other correlations: warmer and wetter conditions paved the way for the Vikings of Scandinavia to expand beyond their homes into Iceland, Greenland, and even the Americas. A cold spell around the year 1300 coincides with widespread famine across Europe. Historians believe this famine was a critical factor in the spread of the Black Death in AD 1347.

This systematic study of European history reveals that neither the mighty Romans nor the civilizations followed were immune to changes in climate. The team’s results also provide strong evidence of a link between climate change and political and economic wealth. Climate change in human history has had devastating effects on social, political, and economic growth. What effects could it have on our future?

Anne Holden, a docent at the California Academy of Sciences, is a PhD trained genetic anthropologist and science writer living in San Francisco.

Image: Jimmy Walker/Wikimedia