In astronomy, photometry is a way of measuring the flux of the electromagnetic radiation of an astronomical object. Filter photometry basically means that you split the collected light from a celestial object only into a few wavelength bins that are defined here by the commonly used filters in the visible called 'B, V, I Johnson–Cousins filters' [or blue, green and red colour bins]. The advantage of this approach is that lots of photons are gathered per bin, meaning a good signal-to-noise ratio is achieved, which in turn means that it may be possible to characterize dimmer planets. The researchers use this method to identify planets that have surfaces similar to those on Earth that harbour life. This is done by plotting the blue–green versus blue–red bins using customized filters, creating what is known as a "color–color diagram". While the technique does not provide the finer details of a planet, it can very easily be used to put together a follow-up prioritized "target list" of planets that should be studied in detail with spectroscopy.
A way of looking for these extreme environments is to study the "albedo" of a planet – its reflectivity as a function of wavelength. For example, snow has a high albedo, meaning that it reflects well, while water has a low albedo and so does not reflect as well. A previous study, conducted in 2003, compared the colour–colour diagrams of rocky and Jupiter-like planets in our solar system to see whether they were the same – they were not. That study concluded that a color–color diagram can be used to make a first-order basic characterization of a planet's nature. Siddharth Hegde of the Max Planck Institute for Astronomy in Germany and colleague Lisa Kaltenegger from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts extended this idea to rocky exoplanets based on the assumption that these habitats best determine the environmental limits for harboring Earth-type extremophiles.
The method is similar to another already used by exoplanet hunters who look for the "red-edge" – a telltale sign of vegetation – in the spectra of planets. This is a large and abrupt change in the absorption of light by plants that occurs at about 700 nm. At shorter wavelengths, chlorophyll absorbs very strongly and therefore plants reflect little light; above 700 nm, chlorophyll does not absorb light, which means that leaves are able to reflect much more sunlight back into space. Combining such spectral readings with color–color diagrams could clearly indicate if a planet has any Earth-like life, or is capable of harboring it. In the future, the researchers are keen to study possible changes in a planet's atmosphere caused by different kinds of extremophiles that might inhabit its surface – for the moment, their model assumes the extremophiles do not affect the atmosphere significantly. "Maybe, with the help of biologists who culture such extremophiles in the lab, we can find out if there are gases in the atmosphere that can tell us whether such surfaces really harbour life," muses Hegde.
Bursts of gamma rays usually occur far out in space, near black holes and other high-energy cosmic phenomena. Scientists were surprised when, in the mid-1990s, they found powerful gamma-ray flashes happening in the skies over Earth. Powerful natural particle accelerators in the atmosphere are behind the processes that create lightning. Terrestrial gamma rays (TGFs) result from this particle acceleration. Individual particles in a TGF contain a huge amount of energy, sometimes more than 20 mega-electron volts. The aurora borealis, for example, is powered by particles with less than one-thousandth as much energy as a TGF. But what causes a TGF's high-energy flashes? Does it trigger lightning--or does lightning trigger it? Could it be responsible for some of the high-energy particles in the Van Allen radiation belts, which can damage satellites?
A tiny little satellite, called CubeSat or 'Firefly - the size of a milk carton whirling in space - will soon find out. The CubeSat will look specifically for gamma-ray flashes coming from the atmosphere, not space, conducting the first focused study of TGF activity. Firefly will carry a gamma-ray detector along with a suite of instruments to detect lightning and will return the first simultaneous measurements of TGFs and lightnings. When thunderstorms happen, powerful electric fields stretch upward for miles, into the upper atmosphere. These electric fields accelerate free electrons, whirling them to speeds that are close to the speed of light. When these ultra-high-speed electrons collide with molecules in the air, they release high-energy gamma rays as well as more electrons, starting a cascade of electrons and TGFs. But unlike lightning, a TGF's energy is released as invisible gamma rays, not visible light. TGFs therefore don't produce colorful bursts of light like many lightning-related phenomena. But these unseen eruptions could help explain why brilliant lightning strikes happen.
USGS Earthquake Hazards Program, responsible for monitoring, reporting, and researching earthquakes and earthquake hazards...
This map represents the 1079 earthquakes with magnitudes higher than 2.5 that have occured in the last 30 days. You can customize the map to display different data at any scale. There is detailed information about each earthquake in this great dataset.