After twenty years in space (launched 10 years Bi, Before iPhone), traveling over a billion KM, and returning data for 13 years from more than a light-hour from Earth, the Cassini Spacecraft ended its mission this week.
The project has accomplished lots of amazing science, represented by 3,948 papers so far. There will surely be a few more—lets go for 5K papers!
The end was a planned dive into the atmosphere of Saturn, collecting a few more bits of data on the way down, and assuring the complete destruction of the spacecraft.
As has been explained before, the spacecraft needed to be vaporized to prevent even the slighted chance that it might contaminate the area with Earth microbes. Aside from not wanting to harm any life that might exist on the moons or dust, we also don’t want to accidentally leave something that a later spacecraft might find and not realize was inadvertently sent from Earth.
(Which, if you think about it is way, way cool. How many human endeavors have to worry about the possibility of contaminating alien ecosystems, even in principle?)
Detecting these compounds is difficult because rocks are usually contaminated with younger chemicals (prominently including “anthropogenic petroleum products”) which swamp the faint older deposits. The researchers carefully screened out known contaminants, in order to measure the proportions of steranes and hopanes in the rocks. These are markers for eukaryotic cells, so the data indirectly indicate the predominance of bacteria in the environment.
They link these studies to current understanding of paleoclimate. They find evidence for a remarkable story. Roughly 700 million years ago was “Sturtian snowball glaciation”, an extreme ice age that froze the oceans all the way to the bottom. Before this period, eukarytes predominated, and they died back dramatically during the 100 million year ice age.
At the end of the Sturian, the abundance of bacteria increased, reaching modern abundance within a few tens of million years. Then something happened that enabled Algae to overcome the cyanobacteria, and eventually flood the world with oxygen and animals like us.
The researchers suggest that the glaciation and subsequent melting flooded the oceans with nutrients ground up by the ice cover, which eventually tipped the balance in favor of algae. They offer a possible scenario for this transition. At some point, algae evolved as a hybrid eukaryte engulfing a cyanobacteria, and thrived. This led to rapid evolution of animals that feed on algae.
If this scenario is correct then algae emerged and survived, but only came to dominate the oceans after a billion years. If so, then an episode of extreme global climate change probably led the rise of the biochemistry and ecology that we need to exist.
This study is very interesting, but far from conclusive. Even assuming the data is correct, it still isn’t clear whether the emergence of algae really triggered the evolution of animals, or how other factors were involved..
Still, this is a reminder that the world we see is scarcely the only possible way things could work. It is also makes us realize just how much deep history is floating around in our own cells—we are descended from life that thrived on a radically alien Earth.
Jochen J. Brocks, Amber J. M. Jarrett, Eva Sirantoine, Christian Hallmann, Yosuke Hoshino, and Tharika Liyanage, The rise of algae in Cryogenian oceans and the emergence of animals. Nature, advance online publication 08/16/online 2017. http://dx.doi.org/10.1038/nature23457
Friend, Tim, The Third Domain: The Untold Story of Archaea and the Future of Biotechnology, Washington, DC, Joseph Henry Press, 2007.
With a long-term mission to visit and measure everywhere in the Solar System, NASA has not ticked off the easy stuff—Earth orbit, Moon, Mars, orbiting all the Planets.
There are plenty of places we really want to visit, but haven’t been able to. Cold places like the ice moons. And really hot places like the Sun and the surface of Venus.
In the case of Venus,several spacecraft have orbited and are orbiting, and a handful of probes have reached the surface–just barely. The surface is hot, over 400 degrees C, and the pressure is a crushing 90 atmospheres. Most electronics simply don’t work at these temperatures. And it’s very cloudy, so solar power is minimal. And so on.
In short, conventional engineering has little chance. To date, the record time to failure is 2 hours, set by a heroically insulated Vernera 13 probe in 1982. Building such extreme systems is hard and very expensive.
There is no way to make a rover to explore Venus. What’s to be done?
Alternative locomotive ideas include wheels and tank treads.
But moving around is the least of the problems. How do you collect data?
In an interview with Evan Ackerman, they report several intriguing ideas under development.
First of all, mechanical calculation and number storage should be doable. And rough forms of obstacle avoidance are well known, too. (Toy cars navigate around furniture by bumping and backing up, no?.)
But if you had some data, how would you return data to Earth (i.e., to an orbital relay)? One possibility would be some kind of hard copy (e.g., etched into a metal disk), which is then lifted with a balloon and potentially pick up be a high altitude UAV. That sounds cool, but pretty iffy.
Another idea is to do semaphore code with radar reflectors. The orbiter beams radar and the rover reflects back on-off signals are certain wavelengths. This might have a bandwidth of a few bits per second (one way). That’s not much, but it’s a lot more than zero bps! Pretty cool.
They are also trying to develop some kinds of sensors that will work under these conditions. This is difficult and it might be an area where small amounts of exotic high temperature electronics might be used.
This is such a cool design project!
I’m not sure how these ideas will pan out, but this work
If you’re going to go all the way out to Jupiter, and spend months snapping pix, you really, really ought to get some pictures of the Red Spot. The Great Red Spot has been observed since 1830, but never from this close.
We’re all fascinated with the story of the end of the Dinosaurs, which corresponds with a really big impact, and possibly other catastrophes. The death of the dinosaurs is not only a puzzle, it is the event that made room for mammals and puny humans to evolve.
But there was also a mass extinction that cleared the way for the great adaptive radiation of dinosaurs. At the end of the Triassic period, about 200M years ago, there was a massive extinction of animals. The dinosaurs rose after this catastrophe.
This month a team of British scientists published new evidence that there was a huge sequence volcanic eruptions at that time, which would have been devastating for living things. This event has been suspected from other evidence of huge lava flows, global cooling (due to volcanic material in the atmosphere), and, of course, mass extinctions.
The new study uses a new techniques which measures mercury (Hg) in the rocks. This element is highly correlated with volcanic activity, which spews Hg into the air. The mercury falsl out and is incorporated into rock, where it persists for long periods of time–hundreds of millions of years.
Careful measurements indicate high levels of mercury in the period between the extinctions at the end of the Triassic, and the beginning of the Jurassic. In other words, a very clear suggestion that the volcanic disaster caused the extinctions, and the end of the episode was followed by the rise of the dinosaurs.
A key aspect of this work is to trace mercury deposits to many locations around the world. Furthermore, the deposits should be temporally aligned, rising and falling at the same time. These signatures are consistent with large volcanic “pulses”.
The researchers report that the “Hg excursions are recorded in five of the six sections studied”, and that “The onset of Hg enrichment occurred synchronously across the globe, coincident with the end-Triassic extinction and associated global carbon cycle perturbation.“ (p.5)
In other words, there is clear evidence of very widespread effects of volcanism at the precise time of the mass extinctions.
Lawrence M. E Percival, Micha Ruhl, Stephen P. Hesselbo, Hugh C. Jenkyns, Tamsin A. Mather, and Jessica H. Whiteside, Mercury evidence for pulsed volcanism during the end-Triassic mass extinction. Proceedings of the National Academy of Sciences, June 19, 2017 2017. http://www.pnas.org/content/early/2017/06/13/1705378114.abstract
On the last orbit, Cassini imaged my ave-moon Enceladus from close up, and, of course,. earlier observations have sighted probably tectonic and volcanic activity, including plumes of water. (Volcanic activity is a particularly apt link to the namesake giant, who was associated with volcanos and earthquakes.)
Radwan Tajeddine and colleagues report this spring on analysis which suggests that Enceladus has flipped 55 degrees sometime in the past . This analysis is based on data collected in 2005 and later — yes, Cassini has been investigating Saturn for more than ten years now!
The new findings are based on images that show patterns of large “basins”, low areas on the icy surface. Some of the basins are located in a neat great circle, which the researchers suggest that these basins reflect patterns in convection in the liquid interior. In addition to the basins that align with contemporary poles, there are five older basins that are similar but not aligned. These do align with a similar great circle, if the pole were in a location 55 degrees from the current pole. Hence, the hypothesis that Enceladus shifted its rotational poles at some point in the past.
(Please see the paper for the details of their inferences and arguments.)
It isn’t obvious what might have caused this shift in poles. The researchers think that this may be a case of “True Polar Wander”, which can happen in slowly rotating nearly spherical objects (such as icy moons). A redistribution of mass might have led to a new axis of rotation. Considering the watery and slushy interior, this seems plausible, if difficult to verify—without landing there!
Yet one more reason to send out robots to the icy moons.
(I’m not holding my breath for the current US government to support any such project. Trying to roll back history to the nineteenth century means no space program, though that’s the least of the harm that will cause.)