HR 8799 d: Photographed, Not Inferred
Gas giant around HR 8799
It is 1.16 times Jupiter's radius, closest in size to Jupiter, and 3000.0 times Earth's mass. A year there lasts 101.3 years, on an orbit 62.0 times Mercury's distance from the Sun.
HR 8799 from the inside out
Orbit
/
Planet
Radius
13.00 Earth radii
Mass
3000.0 Earth masses
One year
101.3 years
Orbit radius
24.0000 AU
Distance
135 light-years
What the archive holds on this planet
A size. Yes.
A weight, not just a width. Yes.
A density, the one clue to composition. No.
How far out it orbits. Yes.
A temperature someone observed rather than calculated. No.
An eccentricity, so the orbit shape is known. No.
What a direct image buys you
Where it is, how bright it is, and a spectrum taken from the planet directly.
HR 8799 has 4 known planets. A crowded system is worth more than the sum of its planets: the timing of each transit constrains the others.
This is one of the rare planets that has actually been photographed. Fewer than a hundred of the thousands known were found this way, and they are mostly young giants far from their stars.
Found by W. M. Keck Observatory in 2008.
Fewer than a hundred planets have been photographed rather than inferred. Does \
seeing one directly change how real it feels to you?
