About
“I was sitting near the campfire wondering about the stars. Slowly a thought came: The stars are flame, I thought. Then I had another thought: The stars are campfires that other hunterfolk light at night. The stars give a smaller light than campfires. So the stars must be campfires very far away.” — Carl Sagan, Cosmos .
The early humans may not have been far wrong about the stars. We have discovered more than 4000 planets around stars other than our Sun (exoplanets), and we are rapidly discovering more. Browse planet gallery to see real images of all the exoplanets we have discovered so far! What you will see is a vignette of the sky around the star hosting the exoplanet.
It’s possible that some of these planets harbour life. Which one do you think?
Finding exoplanets is hard. Most of the planets listed here have been discovered with one of these four methods:
- Transit — The exoplanet’s orbit takes it crosses directly in front of its host star from our point of view on Earth. When the exoplanet crosses its star, it blocks some of the light and with optical telescopes we can see this drop in the stars brightness. If we see a star’s brightness periodically decrease then there is a good chance we have found a planet!
- Radial velocity — “For every action there is an equal and opposite reaction” — Newton’s third law of motion. The host star exerts a gravitational pull on its exoplanet, so the exoplanet pulls back. This gravitational force from the exoplanet jiggles the star around. When the star moves parallel to our line of sight, we can measure its velocity through spectroscopy. The host star’s spectrum changes due to the Doppler shift. If we see a star moving back and forth periodically it is possible it hosts an exoplanet.
- Microlensing — Gravity bends light. If a star happens to cross directly in front of another star, it acts as a lens. We can observe these lensing events with optical telescopes. It turns out the lensing pattern is very sensitive to exoplanets around the lensing star.
- Direct Imaging — This technique is the most basic but perhaps the hardest. The exoplanet is directly imaged with a telescope by blocking out the host star’s light with a filter (coronagraph).
Each of these methods is sensitive to different planet masses and orbital radii. The remaining few planets were discovered using exotic techniques like pulsar timing (there are planets that orbit neutron stars!). NASA has nice visualisations of each of these methods.
We display each exoplanet as a contour plot of its surrounding starfield. The star in the center of the image hosts the exoplanet (note: a few of the closer exoplanet host stars may not be exactly in the middle of the frame because the stars move). The contours represent brightness linearly, Every contour you cross increases the measured brightness by a fixed amount. The sharp four corners you see in some bright stars are diffraction patterns generated by the telescope. We use contours so we can plot the star fields using a plotter printer:
We also like to plot some of our favourite galaxies and black holes using a HP-7470A plotter printer.
One day we hope to curate a physical gallery of exoplanets. Perhaps the Earth features in an equivalent gallery on another planet…
PLANET GALLERY
Planet gallery is a collaboration between Dylan Freedman and Lawrence Peirson . Planet data is from the open source NASA exoplanet archive .