HD209458b may not sound familiar to the layman, but many astronomers know it well. HD209458b, also known as Osiris, is one of the earliest extra-solar planets, or exoplanets, to have been found. The gas giant fits a category of exoplanets called hot Jupiters. These planets are gas giants, similar in size and mass to Jupiter, but orbit far closer to their parent stars.

Though Osiris is only .69 Jupiter masses, it is more than 250% as large as Jupiter. This puffed up atmosphere is likely a combination of the great heat and enormous tidal forces of the planet orbiting at .045AU. An Astronomical Unit is the mean distance of Earth from the Sun during its orbit -- a bit under 150M kilometers. For comparison, Mercury orbits the Sun at a mean distance of .39AU.

Osiris has been a much-studied planetary body since its discovery and it represents many milestones for the astronomical community. It was the first discovered transiting exoplanet, first proven to have an atmosphere, first shown to have an atmosphere composed of oxygen and carbon with evaporating hydrogen, and one of two planets first observed by spectroscopy. Later, observations would lead some astronomers to believe the planet's atmosphere also contains water vapor.

Now, using the European Southern Observatory's Very Large Telescope, a group of astronomers from MIT and the Netherlands Institute for Space Research at Leiden University have witnessed not only the first exoplanet weather, but the first measured orbital velocity of Osiris, providing necessary data to determine precisely its mass.

Osiris orbits its star, affectionately know as HD209458, in the same way the Moon orbits Earth. The amount of time it takes the planet to make one complete rotation is the same as the time it takes to make one complete orbit -- about 3.5 days in Osiris's case. The planet shows the same face to HD209458 no matter where it is in its orbital cycle. This invigorates the sunny side of the planet to temperatures in excess of 1,000 degrees Celsius. The dark side remains much cooler, and that temperature difference drives a storm of incredible magnitude.

Using the CRIRES spectrograph, an instrument on the VLT, astronomers very accurately measured the speed of carbon monoxide gas streaming from the hot side of the planet to the cool side. The heat-driven winds clocked in between 5,000 and 10,000 kilometers per hour. For perspective, the fastest non-experimental jet-powered aircraft in the world is the SR-71 Blackbird, which officially topped out at 3,326.6 km/h; EF5 tornadoes, the most powerful ever observed, can rip concrete and steel structures apart and significantly damage even the most durable skyscraper structures with wind speeds only slightly above 320 km/h.

Further, the powerful CRIRES made it possible to examine the carbon content of Osiris's atmosphere. The results showed that the atmosphere was high in carbon, similar to Saturn and Jupiter. This could indicate that, though Osiris is much closer to its star, it formed in a similar manner to the two local gas giants.

Such precise measurements of exoplanetary atmospheres could help planetary scientists understand how some of our own Solar System's planets formed as well as find telltale signs of familiar life in the atmospheres of future exoplanets that aren't so unforgiving.