Web edition: June 18, 2012
Print edition: July 14, 2012; Vol.182 #1 (p. 11)
20 hours of fame
Seen in gamma rays, the sun is usually dark. But on March 7, it blazed for 20 hours after a massive solar flare dumped high-energy particles and light into space. “The sky looked completely different,” Stanford University’s Nicola Omodei said on June 11. NASA’s Fermi Gamma-Ray Space Telescope captured the sun’s brief moment in the … sun, and recorded "the highest-energy light ever detected during a solar flare,” Omodei said. Scientists studying the gamma-ray–producing particles determined that instead of only being flung outward by the initial flare-producing shock, the particles were probably also accelerated by reconnecting solar magnetic fields after the event.
Sun’s short-term memory
Scientists trying to forecast peaks in solar cycle activity have generated vastly variable estimates, ranging from Wimpy to Hulk. Dibyendu Nandy, from the Indian Institute of Science Education and Research in Kolkata, suggests an explanation for the prognostic failure. “The sun has a very short memory,” he said on June 11. “It forgets its history of past activity.” That’s because a process called “turbulent pumping” mixes the solar magnetic field and erases “memories” of past cycles of activity. This mixing makes previous solar cycles bad indicators of future intensity. Instead, Nandy suggests that solar maximums, or periods when the sun has its highest number of sunspots, can be reliably predicted only using the previous minimum — which means the sun remembers its own history for just 5.5 years.
Getting to know the dwarfs next door
Astronomers studying M dwarfs, the most abundant of our stellar neighbors, are beginning to understand more about how these redder, dimmer stars evolve and age. That understanding is important because these stars are likely to be common hosts of exoplanets. On June 12, Scott Engle of Villanova University reported that an M dwarf’s magnetic field betrays the star’s age, which can theoretically reach 100 billion years. Aging stars lose mass and spin more slowly, reducing the magnetic field strength in a predictable way — a relationship Engle discovered after studying M dwarfs in binary systems with companions of known ages. Older M dwarfs are also expected to emit fewer potentially harmful X-rays and less ultraviolet radiation, which could make an orbiting planet a more comfortable place to live.
Small telescope, big planet
Sometimes, a little eye turned toward the sky can see big things. In this case, the Kilodegree Extremely Little Telescope — essentially the equivalent of a digital camera — discovered two enormous stellar companions orbiting faraway stars. One of these bodies is a Jupiter-sized planet orbiting a star bright enough to allow scientists to study the planet’s atmosphere. The other, a big brown dwarf, is “something that has never been seen before,” said Ohio State University graduate student Thomas Beatty on June 13. Like NASA’s Kepler spacecraft, KELT looks for dips in light caused by bodies passing between a star and Earth. KELT-1b, the brown dwarf with a mass equivalent to 30 Jupiters, is one of these star-dimming objects. It circles its star in just 29 hours, receiving 6,000 times the amount of sunlight that Earth gets. “It sort of resets the bar for weird,” Beatty said.
Small planets don’t mind metal-poor stars
Smaller planets tend to live around stars with variable metal content, being equal-opportunity inhabitants of stellar systems that are both metal-rich and metal-poor. This nonpreference is unlike that of Jupiter-sized planets with close-in orbits, which are devoted metalheads that associate primarily with metal-rich stars. In stellar astronomy, “metal” refers to any element heavier than helium. Scientists spied the differing characteristics of the two groups after surveying more than 200 planet candidates in the Kepler field and correlating the planets’ sizes with their host stars’ metal content. The result, reported June 13 at the meeting and online in Nature, suggests that smaller planets form more easily and earlier in a star’s evolution than Jupiter-sized planets. “They could be widespread in our galaxy,” said study coauthor Lars Buchhave of the University of Copenhagen in Denmark.
Weird and distant planet
It’s not just their names that are weird. The dwarf planet Quaoar (Kwa-war) and its satellite Weywot present some unusual characteristics. Quaoar, which orbits the sun at roughly 40 times the Earth-sun distance, is much denser than expected. Weywot takes a more oval-shaped path around Quaoar than it should, if theories describing satellite formation apply to the two tiny Kuiper Belt bodies. Both of these characteristics suggest the system formed after an unusually violent collision blasted away Quaoar’s outer icy sheath, leaving behind a dense chunk of rock. And Weywot, instead of condensing from the resulting debris disk, was borne of a large fragment — the remainder of an “unusually high velocity collision,” said Wesley Fraser of Canada’s Herzberg Institute of Astrophysics on June 13.
Solar flare: N. Omodei et al. Fermi LAT observation highly energetic impulsive solar flares. 220th Meeting of the American Astronomical Society in Anchorage, Alaska, June 13, 2012. [Go to]
Sun’s memory: D. Nandy and B. Karak. The sun has a short memory: Turbulent pumping of magnetic flux reduces solar cycle memory and precludes long-term predictions. 220th Meeting of the American Astronomical Society in Anchorage, Alaska. Poster presentation, June 11, 2012. [Go to]
M dwarfs: S. Engle et al. Anchoring dM star age-rotation-activity relationships and assessing planetary habitability. 220th Meeting of the American Astronomical Society in Anchorage, Alaska. Poster presentation, June 12, 2012. [Go to]
Extremely Little Telescope: T. Beatty et al. The KELT-North transit survey’s first planet detections. 220th meeting of the American Astronomical Society, Anchorage, Alaska. Oral presentation, June 11, 2012. [Go to]
Metalheads: D. Latham and L. Buchhave. Small planets do not require a metal-rich environment. 220th meeting of the American Astronomical Society, Anchorage, Alaska. Oral presentation, June 13, 2012. [Go to]
Quaoar: W. Fraser et al. Tidal evolution of the Quaoar-Weywot system. 220th meeting of the American Astronomical Society, Anchorage, Alaska. Oral presentation, June 11, 2012. [Go to]