On the Horizon: news from the frontiers of science

A distant comet brightens the night sky, scientists experiment with the world's hottest chili pepper, and how soil effects autumn leaves

Comet brightens the night sky

Skywatchers are enjoying an unexpected treat: Comet 17P/Holmes has blossomed from an invisible object some 25,000 times too faint to be viewed with the naked eye to naked-eye brightness in less than a week.

The comet appears in the constellation Perseus as a yellowish "star" near the end of Perseus's left arm, as seen from Earth. It is readily visible through binoculars even with bright moonlight and through all but the worst light pollution, according to editors at Sky & Telescope magazine. And in areas with really dark skies, people have reported seeing it with the naked eye.

The sudden brightening is not unheard of for this comet, discovered in 1892. It brightened, then dimmed, then brightened again between 1892 and 1893. It swings around the sun once every seven years, at a distance of about 200 million miles. Astronomers are puzzling over what has caused the outburst of light. One possible explanation: The comet's approach to the sun has warmed it and caused its surface to crack, leading to an outburst of fresh dust and gas.

Bite this pepper at your own risk

When it comes to spices, chili peppers rank somewhere between mild taste sensation and criminal assault. Now, two plant scientists at New Mexico State University describe what may rank as the most notorious chili of all: the Bhut Jolokia, from Assam, India.

Rumor had it that Bhut Jolokia was the hottest of the hot, but no one had put it to the test. The New Mexico State team, led by Paul Bosland, received a sample seed in 2001. But it took three years of careful cultivation to grow enough of the chilies to provide the seeds needed for detailed, repeated field experiments.

The duo measured this fiery fruit's hotness at a record-breaking 1 million Scoville units, the standard measure of a chili's perceived "heat." By comparison, Jalepeños that grace tacos or salsa only reach 2,500 to 10,000 Scoville units. According to the Guinness Book of World Records, the previous hotshot – a variety of Habanero chili called Red Savina – reaches 577,000 Scoville units.

The researchers also were interested in Bhut's ancestry. Using DNA analysis, they concluded that the chili is a derivative of Capsicum chinense, a type that includes Scotch Bonnet peppers. And it appears to have a bit of Capsicum frutescense, which includes Tabasco peppers, thrown in for good measure. The study appears in the current issue of HortScience, a journal of the American Society for Horticultural Science.

Soil's effect on autumn leaves

This time of year, broad-leaf trees throughout the northern hemisphere are turning their characteristic yellows, oranges, and reds. The pigments protect the leaves as they produce a final batch of nutrients that will be stored in the trees' roots over winter.

Now, a researcher with the McDowell Mountain Regional Park near Phoenix suggests that the intensity of those colors may have as much to do with the soil a tree grows in as with the species of tree itself.

Researcher Emily Habinck surveyed a section of forest in a nature preserve outside of Charlotte, N.C., while a grad student at the University of North Carolina. She found that in places where the soil was low in nitrogen and other nutrients, sweet-gum and red maples produced large amounts of a red pigment compared with trees in more nutrient-rich areas. The mechanism apparently allows the leaves to survive longer into the fall so they can deliver the right amount of nutrients to tree roots.

The work bolsters results from a study in 2003 that hinted at how important the production of red pigment can be. Montana State University's William Hoch used genetic techniques to block red-pigment production in red-leafed plants. When he did, the leaves succumbed far faster to the weaker fall sunlight and so delivered less nutrients to plant roots. The results of Ms. Habinck's work are being presented at this week's meeting of the American Geological Society in Denver.