This is Exoplanet Radio.
I'm Tony Darnell.
On September 9, 1999, a team of
astronomers from the High Altitude Observatory made a
groundbreaking discovery.
Using the radial velocity method, they
detected a massive Jupiter-sized planet orbiting a
Sun-like star, HD 209458.
This was the first exoplanet to be
discovered using this method, and since that fateful
day, this system has become a champion of firsts.
The planet is HD 209458 b, and nicknamed
Osiris after the Egyptian god of the underworld.
Osiris is a fitting nickname for this planet as it is a very hot and hostile world.
HD 209458 b orbits its star very closely,
and its surface temperature is estimated to
be around 1000 degrees Celsius.
This makes it too hot for liquid water to
exist on its surface, and it is unlikely to
be habitable.
Even so, this planet is remarkable in many ways.
It occupies first place in a long list of discovery milestones.
Here are some of the areas Osiris occupies first place.
It is one of the first exoplanets to be
discovered using the transit method, which means that
astronomers were able to detect it by
observing how its star's light dimmed as the planet
passed in front of it.
This was a major breakthrough, as it showed
that it was possible to directly detect exoplanets.
In fact, seeing its transit makes it the
first exoplanet to be detected by more than one
method of both transit and radial velocity.
Further, it was the first planet to have its
orbital speed measure, allowing astronomers
to determine its mass directly.
Osiris is also the first exoplanet to have its atmosphere directly detected.
In 2001, astronomers using the Hubble Space
Telescope were able to measure the absorption
of light from HD 209458 b's atmosphere.
This allowed them to identify the presence of sodium and other elements.
And in 2007, astronomers from the Lowell
Observatory found evidence of water vapor in the upper
atmosphere.
Another first.
These observations were a major breakthrough in exoplanetary research.
It showed that it was possible to learn more
about the composition of exoplanet atmospheres
and to search for biosignatures, which are
molecules that could be indicative of life.
This is also the first exoplanet to be observed losing its atmosphere.
Astronomers have detected a large plume of hydrogen gas escaping from the planet.
This is likely due to the intense heat and
stellar winds from the star stripping it away,
leaving a stream of material behind it.
The discovery of the evaporating atmosphere
showed that some exoplanets could actually
lose their atmospheres.
And this could have a significant impact on their habitability.
This exoplanet, some 157 light years away,
has single-handedly had a profound impact
on our understanding of exoplanets and the search for life beyond Earth.
It has advanced our understanding of other
worlds outside our solar system, perhaps more
than any other exoplanet we've seen.
It has shown that it is possible to directly
detect exoplanets and their atmospheres, find
out what they're made of, and that some
exoplanets are actually losing their atmospheres.
The discovery of HD 209458 b was a major
inspiration for the search for life beyond Earth.
Astronomers now realized what was possible
when studying other worlds in the distant
galaxy.
Although OSIRIS is not a good candidate
for life, its discovery showed that there may
be many other exoplanets out there that are more habitable.
Exoplanet Radio is produced by Deep
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