A new video shared on YouTube is one of the most amazing things we’ve ever seen in planetary science.
The video shows four points of light moving in partial concentric circles around a black disk at their center. What you are actually looking at is a planetary system.
The four dots are exoplanets, with the black disc obscuring their star, 133.3 light-years from Earth. The partial circles are their orbital motions, a time frame compiled from 12 years of observations.
The star is HR8799, and In 2008 its exoplanets were the first system (not the first exoplanet, it was 2M1207b in 2004) astronomers had never seen directly.
Since then, astronomer Jason Wang of Northwestern University has been watching it avidly. He compiled these observations in a time frame – not for any scientific reason, but simply because it’s super awesome.
“It is generally difficult to see the planets in orbit”, Wang says.
“For example, it is not clear that Jupiter or March orbits around our sun because we live in the same system and don’t have a top-down view. Astronomical events happen too quickly or too slowly to capture on film.
“But this video shows planets moving on a human time scale. I hope it lets people enjoy something wonderful.”
The current count of confirmed exoplanets – these are extrasolar planets, or planets outside the solar system – numbers more than 5,200but we never saw most of them.
Astronomers mainly find exoplanets through indirect methods, studying the effect of the exoplanet on the host star. Regular, faint dips in the starlight indicate that an orbiting exoplanet is passing between us and the star; faint changes in the wavelength of light from the star indicate the gravitational interaction between the exoplanet and the star.
The reason for this is that it is actually extremely difficult to see an exoplanet directly. They are very small and very dim compared to their host star; any light they emit or reflect is usually engulfed in the star’s fiery light.
Occasionally, however, we get lucky. The exoplanets are large enough and separated from their star, and the system is oriented in such a way that, if the light from the star is blocked, or occulted (which is why HR8799 appears as a black disk), we can see them like little drops of accompanying light.
It’s even rarer to see them performing their complex planetary struts, simply because the time scales of the orbits involved are far longer than the time since scientists directly spotted the first exoplanet.
But Wang and his team now have enough observational data from HR8799 for a time frame that shows partial orbits, and that’s what he compiled.
“There’s nothing to be gained scientifically from watching orbiting systems in time-lapse video, but it helps others appreciate what we’re studying,” Wang says.
“It can be difficult to explain the nuances of science with words. But showing science in action helps others understand its importance.”
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Observations were collected using the WM Keck Observatory, and Wang applied adaptive optics to correct for the distorting effect of Earth’s atmosphere.
The time-lapse was also processed to correct for temporal jumps between data, showing the smooth orbital motion of the four exoplanets.
The 12 years of observation were sped up in just 4.5 seconds.
Here’s what you’re looking at. The black circle in the center is the 30 million year old young star, about 1.5 times the mass and 4.9 times the luminosity of the Sun.
The innermost exoplanet is HR8799e, with a mass of 7.4 Jupiters orbiting at a distance of 16.25 times the Earth-Sun separation, or astronomical units, for an orbital period of 45 years. Scientists were able to analyze the light from this exoplanet to determine that it is a storm ravaged baby gas giant.
Moving outward, HR8799d has the mass of 9.1 Jupiters and orbits at 26.67 astronomical units for an orbital period of 100 years.
HR8799c has a mass of 7.8 Jupiters, orbiting at a distance of 41.4 astronomical units (just a little wider than the separation between the Sun and Pluto) for an orbital period of 190 years. He has water in its atmosphere, scientists have found.
Finally, HR8799b points at 5.7 Jupiters, with a separation of 71.6 astronomical units and an orbital period of 460 years.
But we are far from done with the HR8799 system.
Although, according to Wang, the time frame itself may not be scientifically revealing, Keck’s data collection certainly is.
An article published last December discovered the possible existence of a fifth exoplanet, smaller and closer to the star than its sisters. The candidate is estimated to be around 4 to 7 times the mass of Jupiter, orbiting at a distance of between 4 and 5 astronomical units, making it harder to spot directly.
And Wang and his colleagues are working hard to analyze the system light. They hope to be able to obtain detailed information about the composition of not only the star, but also the worlds around it.
“In astrophysics, most of the time we perform data analysis or test hypotheses,” Wang says.
“But that’s the fun part of science. It inspires awe.”