Space explained
Orion Nebula, Rosetta and dark matter: three NASA images
Between 24 and 26 October NASA published Rosetta's selfie, a dark matter simulation and the Orion Nebula, M42, which is visible to the naked eye.
In brief
NASA published three astronomical images between October 24 and 26: the Great Orion Nebula (M42), 1500 light-years away and visible to the naked eye; Rosetta's selfie from October 7, 2014, taken 16 kilometers from comet 67P; and a dark matter simulation from the Dark Universe show at the Hayden Planetarium.
Key points
- M42, the Great Orion Nebula, lies 1500 light-years away and spans about 40 light-years.
- The nebula is visible to the naked eye near the three stars of Orion's belt.
- Rosetta's selfie was taken on October 7, 2014, 16 kilometers from comet 67P/Churyumov-Gerasimenko.
- The Rosetta image was the last from the CIVA camera before the separation of the Philae lander, which took place on November 12, 2014.
- Dark matter is no longer considered the strangest source of gravity in the universe: that is now dark energy.
The Great Orion Nebula is also known as M42. It is one of the most famous stellar nurseries in the entire sky. It lies just 1500 light-years away and spans about 40 light-years. NASA’s Astronomy Picture of the Day dedicated the image of Monday 26 October to it. On the two previous days the column had published a self-portrait of the Rosetta probe at comet 67P, on Saturday 24, and a dark matter simulation, on Sunday 25. The column publishes every day an astronomical photograph or visualization with a popular-science explanation.
Rosetta’s selfie from 472 million kilometers away
On October 7, 2014, the Rosetta probe took a self-portrait. It was the European Space Agency’s (ESA) comet hunter. It was about 472 million kilometers from Earth, more than three times the Earth-Sun distance. The probe, however, was only 16 kilometers from the surface of comet 67P/Churyumov-Gerasimenko, a minimal distance on a cosmic scale. In the image, the mission selfie published by ESA, dust and gas escape from the comet’s curious double-lobed nucleus. Sunlight glints off one of the 14-meter solar panels.
The photo comes from the combination of two exposures, one short and one long. The exposures were taken with the CIVA camera system, installed on the Philae landing module. The lander was still attached to the mother probe, called the orbiter. It was the last image from Philae’s camera before separation, which took place on November 12, 2014. The chosen landing site was on the visible hemisphere of the smaller lobe of the nucleus. Immediately after separation, the lander took one final photo toward the orbiter. Then the descent began.
The invisible web of dark matter
On 25 October the column had shown a frame from the Dark Universe show at the Hayden Planetarium of the American Museum of Natural History. The frame came from a dark matter simulation. The filaments of this invisible matter, drawn in black, spread through the universe like spiderwebs, while the rare clusters of ordinary matter appear in orange. The simulations match astronomical observations statistically.
According to NASA, the gravity of dark matter is the main explanation for the rapid rotation of galaxies. It also explains their fast orbits within clusters. It further explains the strong deflection of light by gravitational lenses. One additional detail: dark matter is no longer considered the strangest source of gravity in the universe. That title now belongs to dark energy, a more uniform repulsion that appears to dominate the expansion of the entire universe.
Where to find the Orion Nebula in the sky
The image of the Great Orion Nebula uses assigned colors. The emission of hydrogen, the most abundant element in the universe, highlights veils and filaments of dust and gas. These surround young, hot stars. The nebula contains many stellar nurseries, stellar jets spewing material at high speed, and a bright open cluster of stars known as the Trapezium. It can be seen with the naked eye, near the three stars of Orion’s belt, one of the easiest constellations to recognize. The nebula lies in the same spiral arm of our galaxy as the Sun.
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