Tag Archives: glow

Twinkle, twinkle, little … moon? Jupiter’s icy moon Europa glows in the dark, researchers find

Europa, the frozen but ocean-filled moon that orbits Jupiter is bombarded by a relentless flux of radiation. Day in and day out, Jupiter flings electrons and other particles towards it. These particles hit the ice and salt-rich surface of Europa, creating a soup of complex interactions that produce something otherworldly: they make Europa glow in the dark.

This artistic illustration of Jupiter’s moon Europa shows how the icy surface may glow on the side facing away from the Sun (like the Earth’s moon, Europa is tidally locked so one side always faces Jupiter and one side always faces away). Variations in the glow and the color of the glow itself could reveal information about the composition of ice on Europa’s surface. Credit: NASA/JPL-Caltech

A song of ice and radiation

Cold Europa is already a hotspot of interest for astronomers. Although it is a frozen desert on the surface, astronomers believe it harbors liquid water beneath its icy crust, and based on what we know about its chemical make-up, it seems like a promising candidate for hosting life in this subsurface ocean.

But while the inside of the planed may be teeming with life (it’s probably not teeming, but you know), the surface is interesting in its own right. NASA astronomer Murthy Gudipati and colleagues recreated some of the interactions on Europa’s surface in the lab, exposing salted ice to energetic electrons as they would expect from Jupiter. They found that these interactions trigger a process called electron-stimulated luminescence. Simply put, it glows in the dark.

It’s an unusual process. You may be tricked into thinking it’s common for moons to glow by looking at our very own moon, bright on the night sky. But our moon isn’t glowing, it’s merely reflecting light from the Sun. Meanwhile, Europa truly produces its own light, even on the side that’s turned away from the Sun.

The surface of Europa is covered in cracked and ridged ice. Imge credits: NASA/JPL

This is more than just a cool factoid that researchers have found about Europa. The work presented here is important for understanding Europa’s surface chemical composition and mineralogy, which in turn affect its habitability.

“We were able to predict that this nightside ice glow could provide additional information on Europa’s surface composition. How that composition varies could give us clues about whether Europa harbors conditions suitable for life,” said JPL’s Murthy Gudipati, lead author of the work published Nov. 9 in Nature Astronomy.

“If Europa weren’t under this radiation, it would look the way our moon looks to us—dark on the shadowed side,” Gudipati adds. “But because it’s bombarded by the radiation from Jupiter, it glows in the dark.”

What science is all about

The salty compounds react differently to the radiation and emit their own unique glimmer. By analyzing these glimmers at different wavelengths, astronomers can connect them to their “signatures” and assess the chemical make-up of the moon. This came as a bit of a surprise: researchers didn’t expect to see variations in the glow itself tied to different ice compositions. It was, the researchers call it, serendipity.

“Seeing the sodium chloride brine with a significantly lower level of glow was the ‘aha’ moment that changed the course of the research,” said Fred Bateman, co-author of the paper. He helped conduct the experiment and delivered radiation beams to the ice samples at the Medical Industrial Radiation Facility at the National Institute of Standards and Technology in Maryland.

The proposed robot lander on the surface of Europa (artistic depiction) during the Clipper mission. Image credits: NASA/JPL.

So far, the researchers haven’t made any new discoveries about the chemistry of Europa. We’ll have to wait for NASA’s upcoming Europa Clipper mission, which will observe the moon’s surface over multiple flybys. These flybys (and the planned robot lander) could map Europa’s chemistry and gain insights about the sub-surface ocean (especially its salinity).

It’s uncommon for a lab experiment to be help a space mission know what to prepare for, but this is exactly what science is all about, says Gudipati.

“It’s not often that you’re in a lab and say, ‘We might find this when we get there,'” Gudipati said. “Usually it’s the other way around—you go there and find something and try to explain it in the lab. But our prediction goes back to a simple observation, and that’s what science is about.”

Europa Clipper is set to launch in the mid-2020s and it’s set to be one of the most exciting missions of the decade as it will investigate a part of the solar system that’s promising in regards to extraterrestrial life. Researchers are now reviewing the findings to see how Clipper’s scientific toolkit could detect variations in the moon’s glow.

Journal Reference: Laboratory predictions for the night-side surface ice glow of Europa, Nature Astronomy (2020). DOI: 10.1038/s41550-020-01248-1 , www.nature.com/articles/s41550-020-01248-1

Chameleons display fluorescent bones on the skull, study shows

The lizard master of disguise is surely a very special creature, we can all agree. Researchers discovered a new outstanding feature of the chameleon: its bones shine with a blue hue in UV light.

Fluorescent tubercles showing sexual dimorphism under UV light at 365 nm (A–D) and fluorescence in further chameleon genera (E–G). (A) Male Calumma crypticum ZSM 32/2016. (B) Female C. crypticum ZSM 67/2005. (C) Male C. cucullatum ZSM 655/2014. (D) Female C. cucullatum ZSM 654/2014. (E) Brookesia superciliaris, male (only UV light at 365 nm). (F) Bradypodion transvaalense, male (dim light and additional UV light at 395 nm). (G) Furcifer pardalis, male (daylight and additional UV light at 365 nm).

Bioluminescence is not that uncommon among marine creatures and some insects (see fireflies), but most terrestrial animals don’t quite possess this eye-endearing feature. The fact that researchers found biogenic fluorescence in chameleons — an entirely earthbound animal — is surprising.

Male C. globifer (ZSM 141/2016) showing congruent tubercle/fluorescent patterns (from left to right); top row: alive in the field under sunlight, micro-CT scan of head surface (probable edge artefact in cheek region), micro-CT scan of the skull; bottom row: alive in the field under UV light, ethanol-preserved under UV light.

Male C. globifer (ZSM 141/2016) showing congruent tubercle/fluorescent patterns (from left to right); top row: alive in the field under sunlight, micro-CT scan of head surface (probable edge artefact in cheek region), micro-CT scan of the skull; bottom row: alive in the field under UV light, ethanol-preserved under UV light.

“We could hardly believe our eyes when we illuminated the chameleons in our collection with a UV lamp, and almost all species showed blue, previously invisible patterns on the head, some even over the whole body,” said David Prötzel, lead author of the new study and a Ph.D. student at the Bavarian State Collection of Zoology (ZSM).

German biologists found that the small bone bumps on chameleons’ heads fluoresce under UV light in a blueish shade. These tiny bone structures absorb UV radiation through small “windows” in the skin and then emit a soft blue light. Actually, the windows are just metaphorical, because the thin epidermis layer that covers the projections is transparent.

After seeing their shimmer under UV-lighting, scientists performed microCT scans and matched the small bone tuberosities to the blue colored pattern.

The fact that bones fluoresce under UV conditions was long-known. But using this phenomenon to intentionally fluoresce different body parts surprised the authors, as it was the first time scientists had encountered such a feature.

Okay, okay, but what’s the deal with all this effort to display such a multitude of colors, even fluorescence?

The myth that chameleons use color-change as camouflage has been debunked. A new theory states that these reptiles use skin color-shifting as a way to communicate with their kin. Taking into consideration that most males from the Calumna genus have significantly more fluorescent tubercles than the females, researchers suppose that their goal is to attract mates. Blue, being a rare color in the forest, should be quite eye-catching in this regard.

The well-known panther chameleon (Furcifer pardalis) which is also popular as a pet, shows fluorescent crests on the head. (David Prötzel; ZSM/LMU)

Another interesting observation is the distribution of fluorescence among different genera of chameleons. Researchers discovered that forest-living species are more prone to exhibit glowing tubercles than species which live in open environments.

“As shorter (UV, blue) wavelengths are scattered more strongly than longer wavelengths the UV component under the diffuse irradiation in the forest shade is relatively higher compared to the direct irradiation by the sunlight,” the authors write in the journal Nature.

“Consequently, using UV reflections for communication is apparently more common in closed habitats than in open habitats, as has been shown in chameleons of the genus Bradypodion.”