Surprisingly Bright Cloud Systems and Extreme Storms on Uranus Puzzle Astronomers

Infrared images of Uranus at wavelengths of 1.6 (left) and 2.2 microns (right), that were obtained on Aug. 6, with the Adaptive Optics system on the 10-meter Keck II telescope on Mauna Kea in Hawaii. The white spot is an extremely large storm that was brighter than any feature ever recorded on the planet in these wavelengths. The cloud at the lower-right limb of the planet, grew into the large storm that was seen by amateur astronomers at visible wavelengths. Image Credit: Imke de Pater (UC Berkeley) & Keck Observatory images

Infrared images of Uranus at wavelengths of 1.6 (left) and 2.2 microns (right), that were obtained on Aug. 6, with the Adaptive Optics system on the 10-meter Keck II telescope on Mauna Kea in Hawaii. The white spot is an extremely large storm that was brighter than any feature ever recorded on the planet in these wavelengths. The cloud at the lower-right limb of the planet, grew into the large storm that was seen by amateur astronomers at visible wavelengths. Image Credit: Imke de Pater (UC Berkeley) & Keck Observatory images

If there’s a planet in the Solar System that could justifiably feel neglected, that would be Uranus. Famous for being unique among the rest of the planets because of its rotational axis which is almost parallel to the plane of the ecliptic, causing it to essentially“roll” on its side in its orbit around the Sun, this distant cyan-tinted ringed world has nevertheless earned the definition of the “boring” planet, largely due to the fact that its disk appeared almost featureless and ‘bland’ to the electronic eyes of NASA’s Voyager 2 spacecraft during the latter’s historic close fly by in January 1986. Yet, despite this unjust reputation, Uranus is a greatly fascinating and enchanting world full of well-kept, intriguing secrets, whose study could turn to be key towards a deeper understanding of our Solar System as well as those around other stars. Now, as if wanting to correct the ill-informed description with which it had been associated for decades, Uranus unexpectedly became increasingly active in recent months, displaying enormous and highly visible bright cloud features and extreme storms deep in its atmosphere, while leaving astronomers completely puzzled over the cause of these unusual weather phenomena.

This surprising weather activity on the distant giant planet was first observed in early August by a team led by Dr. Imke de Pater, professor and chair of astronomy at the University of California, Berkeley. Using the Adaptive Optics system on the 10-m Keck II telescope on Mauna Key in Hawaii, the researchers took a series of images of Uranus in infrared wavelengths at 1.6 and 2.2 microns, which revealed the presence of a total of eight very massive storms that were consisted of clouds that shone very brightly in these wavelengths and were spread over the planet’s northern hemisphere. Further analysis showed that these clouds were laying at different altitudes in Uranus’ atmosphere, but overall they were located well above the planet’s methane cloud deck at the boundary between the upper troposphere and lower stratosphere.

Uranus is the only planet in the Solar System to have a very large axial tilt of 98 degrees relative to the ecliptic plane, causing the planet to 'roll' on its side as it orbits the Sun. Image Credit: M. Showalter/M. Gordon/SETI Institute

Uranus is the only planet in the Solar System to have a very large axial tilt of 98 degrees relative to the ecliptic plane, causing the planet to ‘roll’ on its side as it orbits the Sun. Image Credit: M. Showalter/M. Gordon/SETI Institute

These findings were quite unexpected not least because of the fact that theoretical models had predicted that such a highly visible, increased atmospheric activity on Uranus should mostly happen around vernal equinox in 2007 when the planet’s equatorial regions would again be facing the Sun after decades of cold darkness, only to fade away as time would pass by. Yet, Uranus had exhibited no such extreme storm systems since 2001 when de Pater’s team first began to study the planet with the Keck telescope. And even though many astronomers had also detected various cloud features in the atmosphere of Uranus during the last two decades with the help of ground and space-based telescopes, none had been as massive and as bright as those that were recently discovered by Dr. de Pater’s team, leaving researchers completely baffled. “This type of activity would have been expected in 2007, when Uranus’s once-every-42-year equinox occurred and the Sun shined directly on the equator,” says Heidi Hammel, a senior research scientist at the Space Science Institute in Boulder, Co, and member of de Pater’s team. “But we predicted that such activity would have died down by now. Why we see these incredible storms now is beyond anybody’s guess.”

As exciting as these findings were they proved to be just the appetizer, only to be followed by similar findings that were made by the amateur astronomy community in the following months. Answering to a call by the scientific community for follow-up observations, French amateur astronomer Marc Delcroix and other fellow amateur astronomers photographed the distant giant planet during September and October, leading to the discovery of a different cloud feature that was located deep into the atmosphere, below the planet’s methane cloud deck.”Interestingly, the extremely bright storm seen by the 10-meter Keck II telescope in the near infrared is not the one seen by the amateurs, which is much deeper in the atmosphere than the one that initially caused all the excitement.” says Dr. Lawrence Sromovsky, a planetary scientist at the University of Wisconsin–Madison and member of de Parte’s team. Amateur astronomers had indeed every right to feel proud, for not only they had been able to make these kinds of atmospheric observations on Uranus for the first time, but they managed to complement the discoveries that were being made by professional astronomers as well. “I was thrilled to see such activity on Uranus,” said Delcroix later in a statement. “Getting details on Mars, Jupiter or Saturn is now routine, but seeing detail on Uranus and Neptune is the new frontier for us amateurs and I did not want to miss that. I was so happy to confirm myself these first amateur images on this bright storm on Uranus, feeling I was living a very special moment for planetary amateur astronomy.” These detections by the amateur astronomers subsequently helped researchers to secure some observing time on NASA’s Hubble Space Telescope, which imaged the entire planet on Oct. 14, clearly showing the atmospheric features that had been previously detected by the amateur astronomy community and possible remnants of the one that de Parte’s team had first spotted in early August.

Uranus as imaged by amateur astronomers in visible wavelengths on Sept. 19 and Oct. 2, showing the dramatic appearance of a bright storm on a planet that normally displays only a diffuse bright polar region. Image Credit: Anthony Wesley, Murrumbateman, Australia.

Uranus as imaged by amateur astronomers in visible wavelengths on Sept. 19 and Oct. 2, showing the dramatic appearance of a bright storm on a planet that normally displays only a diffuse bright polar region. Image Credit: Anthony Wesley, Murrumbateman, Australia.

Excitement aside, Uranus’ sudden energetic nature promises to keep the scientific community busy for a long time looking for possible explanations for the planet’s unexpected extreme weather phenomena. “The bottom line is that there’s a lot of dynamic activity in Uranus’ atmosphere and we have really no idea why,” said Dr. de Pater during the presentation of her team’s findings on Nov. 12, at the 46th annual meeting of the American Astronomical Society’s Division for Planetary Sciences in Tucson, Ariz.

In order to learn more about these fascinating discoveries, we contacted Dr. de Pater and had a very interesting discussion regarding her team’s findings.

AmericaSpace: Dr. de Pater, I’d like to thank you for taking the time for this interview to answer some questions for our readers. Would you like to start by telling us more about your research interests and the focus of your work at the University of California?

Dr. Imke de Pater: It’s my pleasure! Well, I’m studying a variety of objects in the Solar System using the Adaptive Optics system at the Keck Telescope and one of those is Uranus, about which we had a recent press release, and I have also keenly observed Neptune, Io, Jupiter’s volcanic moon, as well as Jupiter itself among other things. I’m also conducting radio observations of the Solar System’s giant planets with the Very Large Array in New Mexico”.

AmericaSpace: Your research team has recently announced some very fascinating findings of extreme storms and vast cloud systems in the atmosphere of Uranus. Why are they important?

Dr. Imke de Pater: We have been observing Uranus since about 2001 and we had expected to see increase in clouds close to the 2007 equinox, when the Sun shone directly over the equator. We indeed did see some more clouds back then, and after a while they seemed to decrease in number and intensity. So when we recently observed Uranus, we were amazed by the number of clouds that we saw and also how bright they were at a wavelength of 2.2 microns, relative to the background. But we had never ever seen anything like that before and now, during a period which had been predicted to be much quieter.

AmericaSpace: That is rather strange, because Uranus is thought to lack any adequate source of internal heat in order to power such atmospheric phenomena. Are there any current hypotheses to explain them?

Dr. Imke de Pater: No, none at all. We hope that some theorists will actually take note of this and will start to think about it, but up till now we haven’t heard of any potential explanations. And of course, the other thing is that we’d like to continue observing, to actually see how all this activity will go. Will we see more and more clouds? Will it turn off again and how long are these things going to stay around? We just don’t know. “

A composite Hubble image taken in October 2014, showing the enormous cloud features that were recently detected by both professional and amateur astronomers. Image Credit: NASA/ESA/Imke de Pater (UC Berkeley).

A composite Hubble image taken in October 2014, showing the enormous cloud features that were recently detected by both professional and amateur astronomers. Image Credit: NASA/ESA/Imke de Pater (UC Berkeley).

AmericaSpace: Your team’s observations were also complemented by those made by amateur astronomers. What have been the contributions of the amateur astronomy community in this case?

Dr. Imke de Pater: After we had detected these big, large storms on Uranus, we alerted the amateur astronomy community, because amateur astronomers can now get amazing images using big telescopes. So, they started to observe Uranus and several of them managed to get pretty good images and that actually helped to trigger the Hubble ‘Target of Opportunity’ proposal that we had made, allowing us to get time on the Hubble Space Telescope during October and also in November. The spot that was seen by the amateur astronomers wasn’t not a very bright one similar to what we had seen with Keck. It’s a fainter one and its deeper in the atmosphere. In 5th of August, and again in 6th, we saw a couple of cloud features that were much deeper in the atmosphere than the very bright one that we saw the second day. That one was seen by the amateur astronomers, probably because it was in the right position in the atmosphere and their instruments were sensitive to it. And so, with the Hubble image, we also did see the spot that had been detected by the amateur astronomers and perhaps we have also seen some remnants of the very bright one that we saw with Keck on the 6th of August. But is not as bright any more and we’re still working out to understand what we actually saw, which isn’t altogether too clear.

AmericaSpace: As a planetary scientist, you have been studying Uranus for many years. In light of your studies, what is the current level of our knowledge about this distant, enigmatic world, compared to what we had learned from the Voyager 2 flyby?

We’ve learned a lot more. When Voyager 2 flew by Uranus we didn’t see many cloud features in the atmosphere. Only a few were seen pretty dimly, although at the AAS Division for Planetary Sciences meeting last week, Erik Karkoschka from the University of Arizona put out a press release explaining how he had re-visited the Voyager data. By basically taking out the rotation of the planet, he was able to stack many images together and see cloud features that are very faint and were not seen before. Because the imaging processing techniques had advanced quite a lot since the time of the Voygager flyby, he was able to find more cloud features which gives us a much better idea about the wind profile of Uranus’ atmosphere. So now we have good measurements of the entire wind profile for both the northern and the southern hemisphere which we didn’t have at the time. And there are many puzzling effects there as well.

AmericaSpace: So the reputation of Uranus being a ‘boring’ planet seems to be quite unjust.

Dr. Imke de Pater: “Right, it’s very unjust, cause at the time we just didn’t know.

AmericaSpace: Why is the study of Uranus and Neptune so important in the broader context of the Solar System? What can we learn by visiting these planets?

Dr. Imke de Pater: Uranus and Neptune are quite different. They are much smaller than Jupiter and Saturn and they have a lot more heavier elements in their interior. They are called the ‘ice giants’ not because there is water ice in their interior, but because they are composed of heavier elements and we think that there’s more like an ionic ocean in their interiors which probably generates the magnetic field that surrounds these planets.

An image of Uranus by Voyager 2 after being processed by Erich Karkoschka, a planetary scientist at the University of Arizona, with the help of advanced imaging processing techniques. The end result revealed dozens of previously unseen atmospheric features that were spread over most of the planet's southern hemisphere. Image Credit: Erich Karkoschka/University of Arizona

An image of Uranus by Voyager 2 after being processed by Erich Karkoschka, a planetary scientist at the University of Arizona, with the help of advanced imaging processing techniques. The end result revealed dozens of previously unseen atmospheric features that were spread over most of the planet’s southern hemisphere. Image Credit: Erich Karkoschka/University of Arizona

AmericaSpace: Staying on the same subject, Uranus has been listed as the third highest priority Flagship mission target after Mars and Europa, in the 2013 Planetary Science Decadal Survey by the National Research Council. What is the current status of NASA’s exploration plans for Uranus, if any? Can we expect to see such a planetary mission concept being realised in the foreseeable future?

Dr. Imke de Pater: I doubt it. I think the Europeans are much further along. Basically, they are working on proposals to their space agency in order to get a Uranus mission selected. My guess is that if they are successful in this process, they will try to part with NASA, or at least get some instruments funded by NASA for that mission. So things are indeed moving along, but it usually gets quite a while before a mission like this is selected.

AmericaSpace: In recent years, many mini-Neptune-type exoplanets have been discovered orbiting other stars, indicating that they are quite common in the galaxy. Could this be more of a reason to again visit these types of worlds in our own Solar System?

Dr. Imke de Pater: From the Kepler mission, we now know that exo-Neptunes and exo-Uranus-type exoplanets are more abundant than exo-Jupiters and Saturns. Actually if you go to smaller sizes, similar or a few times that of Earth’s, those are much more abundant in the Universe than Jupiters and Saturns. So for this reason, it is also important to study Neptune and Uranus. And of course those two differ so much in particular due to their heat source and lack thereof respectively, that studying them both really gives an idea of what we might expect to see on ice giant exoplanets around other stars.

AmericaSpace: Dr. de Pater, I’d like to once again thank you for taking the time to answer these questions for our readers and wish you all the best of success with your ongoing research efforts!

Dr. Imke de Pater: Thank you. It was my pleasure.

The ongoing studies by de Pater’s team and others, will hopefully provide us in the future with many more important and fascinating insights about the nature of our planetary family’s distant ice giants, that have been so neglected by space agencies through the years. In the meantime, the recent outburst of activity on Uranus, serves as a reminder that many undreamt treasures could be hiding below apparently ‘bland’ and ‘boring’ appearances, which we can only uncover if we take the time to look beyond the surface.

 

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