Starship Asterisk*

Image Credit: ESO/SPECULOOS Team/E. Jehin

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This image features a comet located in the outer reaches of the Solar System: comet C/2016 R2 (PANSTARRS). As its name suggests, the comet was discovered in 2016 by the Pan-STARRS telescopes in Hawai’i. The new image seen here was captured by a project based at ESO’s Paranal Observatory in Chile named the Search for habitable Planets EClipsing ULtra-cOOl Stars — or SPECULOOS for short.

Comets are balls of dust, ice, gas and rock. When they pass close to the Sun, their ice warms up, turns to gas, and escapes in a process called “outgassing”. This process forms fuzzy envelopes around the comets’ nucleus, called comas, and distinctive tails. Observations from SPECULOOS show that the tail of C/2016 R2 (PANSTARRS) changes dramatically across a single night, making for a dynamic set of images. The image shown here, and accompanying frames in the time-lapse movie, comprise observations taken on 18 January 2018 during the test phase of SPECULOOS’s Callisto telescope, and were taken when the comet was 2.85 AU from the Sun (1 AU being the Earth-Sun distance) and travelling inwards.

This comet is particularly exciting because of the rare compounds and molecules that scientists have detected in its coma: carbon monoxide and nitrogen ions. These compounds give the comet distinctive blue emission lines — so much so that it is nicknamed “the blue comet”. This shy comet only orbits the Sun once every 20 000 years, its most recent approach being in May 2018. This image was taken over a period of time as the telescope tracked the comet’s motion; the bright streaks of light in the background are faraway stars, but the comet and its gaseous coma are all in focus, a testament to the tracking power of SPECULOOS.

Image Credt: ESA/Hubble & NASA, D. Rosario

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The NASA/ESA Hubble Space Telescope sees galaxies of all shapes, sizes, brightnesses, and orientations in the cosmos. Sometimes, the telescope gazes at a galaxy oriented sideways — as shown here. The spiral galaxy featured in this Picture of the Week is called NGC 3717, and it is located about 60 million light-years away in the constellation of Hydra (The Sea Serpent).

Seeing a spiral almost in profile, as Hubble has here, can provide a vivid sense of its three-dimensional shape. Through most of their expanse, spiral galaxies are shaped like a thin pancake. At their cores, though, they have bright, spherical, star-filled bulges that extend above and below this disc, giving these galaxies a shape somewhat like that of a flying saucer when they are seen edgeon.

NGC 3717 is not captured perfectly edge-on in this image; the nearer part of the galaxy is tilted ever so slightly down, and the far side tilted up. This angle affords a view across the disc and the central bulge (of which only one side is visible).

Susanna Kohler wrote:

How does tilting a planet affect its ability to hold on to its atmosphere in the face of intense stellar radiation? The above images are from a series of numerical simulations run by a team of scientists led by Chuanfei Dong (Princeton University), which explore the role of magnetic obliquity — the tilt of the planet’s magnetic field — in regulating the loss of ions from an exoplanet’s atmosphere. In particular, Dong and collaborators modeled Earth-like planets in the habitable zones of two different host stars: a Sun-like G dwarf (top row) and a TRAPPIST-1-like M dwarf (bottom row). The simulation frames above show the ion loss from these two planets with four different tilts: 0°, 45°, 90°, and 135° (columns from left to right). While obliquity doesn’t much affect mass loss for a planet around a Sun-like star, the planet around the M-dwarf loses twice as much mass when its obliquity is oriented at 90° than it does when it’s aligned at 0° — which could matter for such a planet’s potential habitability! For more information on the authors’ conclusions, check out the article below.

• Astrophysical Journal Letters 882(2):L16 (2019 Sep 10) DOI: 10.3847/2041-8213/ab372c
• arXiv.org > astro-ph > arXiv:1907.07459 > 17 Jul 2019 (v1), 31 Jul 2019 (v2)

Image Credit: ESA/Hubble & NASA, P. Erwin

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The galaxy NGC 4380 looks like a special effect straight out of a science fiction or fantasy film in this Hubble Picture of the Week, swirling like a gaping portal to another dimension.

In the grand scheme of things, though, the galaxy is actually quite ordinary. Spiral galaxies like NGC 4380 are one of the most common types of galaxy in the Universe. These colossal collections of stars, often numbering in the hundreds of billions, are shaped like a flat disc, sometimes with a rounded bulge in the centre. Graceful spiral arms outlined by dark lanes of dust wind around the bulging core, which glows brightly and has the highest concentration of stars in the galaxy.