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SpaceX satellites' effect on night sky can't be eliminated, astronomers say – Ars Technica

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Enlarge / Artist’s impression of low-Earth orbit satellites like those launched by SpaceX and OneWeb.

Broadband satellites being launched by SpaceX and other companies will inevitably have a negative impact on astronomers’ ability to observe the night sky, according to a new report by astronomers. There are no mitigation strategies that can completely eliminate the satellites’ impact on astronomical observations—other than not launching satellites at all—but the report includes recommendations for how satellite operators can minimize disruption and how observatories can adjust to the changes.

The report released this week is titled, “Impact of Satellite Constellations on Optical Astronomy and Recommendations Toward Mitigations.” The report resulted from the recent Satellite Constellations 1 (SATCON1) workshop, which was organized jointly by the National Science Foundation’s NOIRLab and the American Astronomical Society (AAS). SpaceX engineers participated in the online workshop, but the report was written by members of the SATCON1 Scientific Organizing Committee and represents their consensus views. The committee members hail from NOIRLab, AAS, the Lowell and Steward observatories in Arizona, the Rubin Observatory in Chile, the University of Michigan, UC-Davis, Smith College, and the Association of Universities for Research in Astronomy (AURA).

The report said:

Changes are required at both ends: constellation operators and observatories. SpaceX has shown that operators can reduce reflected sunlight through satellite body orientation, Sun shielding, and surface darkening. A joint effort to obtain higher-accuracy public data on predicted locations of individual satellites (or ephemerides) could enable some pointing avoidance and mid-exposure shuttering during satellite passage. Observatories will need to adopt more dynamic scheduling and observation management as the number of constellation satellites increases, though even these measures will be ineffective for many science programs.

SpaceX has so far launched over 600 satellites and OneWeb has launched 74. Both companies plan to eventually launch tens of thousands of satellites into low-Earth orbits and provide broadband to areas that lack fast wired service. Amazon is also planning to launch thousands of satellites. Because of their low-Earth orbits (LEO), the satellites will provide lower latency than traditional satellite networks.

Musk predicted no impact

SpaceX CEO Elon Musk said in March that he is “confident that we will not cause any impact whatsoever in astronomical discoveries.” He said the satellites are visible immediately after launching because “they’re tumbling a little bit” and essentially “blink” or “reflect in ways that is not the case when they’re on orbit.” Once satellites stabilize and raise their orbits, they shouldn’t cause problems for astronomers, Musk claimed.

But it’s been over a year since SpaceX began launching broadband satellites, and astronomers have now “accumulated enough observations of constellation satellites like those being launched by SpaceX and OneWeb and run computer simulations of their likely impact to begin to understand the magnitude and complexity of the problem,” the SATCON1 report said.

A wide-field image (2.2 degrees across) from the Dark Energy Camera on the Víctor M. Blanco 4-m telescope at the Cerro Tololo InterAmerican Observatory, taken on November 18, 2019. Several Starlink satellites crossed the field of view.
Enlarge / A wide-field image (2.2 degrees across) from the Dark Energy Camera on the Víctor M. Blanco 4-m telescope at the Cerro Tololo InterAmerican Observatory, taken on November 18, 2019. Several Starlink satellites crossed the field of view.

“If the 100,000 or more LEOsats proposed by many companies and many governments are deployed, no combination of mitigations can fully avoid the impacts of the satellite trails on the science programs of current and planned ground-based optical-NIR [near-infrared] astronomy facilities,” the report said. “Astronomers are just beginning to understand the full range of impacts on the discipline. Astrophotography, amateur astronomy, and the human experience of the stars and the Milky Way are already affected.”

Report authors said they “performed simulations of representative LEOsat constellations” in order to reach their conclusions. Recommendations for minimizing harms to astronomy “are based on work by and collaboration between astronomers and SpaceX,” but these are “intended for a broad audience, and especially the satellite constellation industry as a whole,” the report said.

Altitude is important

The satellites’ impact on astronomy will be affected by their altitude. Satellites orbiting at altitudes below 600km (like those being launched by SpaceX) are not as harmful to observations as those orbiting above 600km (like those launched by OneWeb). Amazon’s plan calls for altitudes of 590km, 610km, and 630km.

“LEOsat constellations below 600km are visible for a few hours per night around astronomical twilight from observatories at middle latitudes, but they are in Earth’s shadow and invisible for several hours per night around local solar midnight, with some satellites visible during the transitions. This visibility pattern causes these constellations to most heavily impact twilight observers,” the report said.

With sub-600km satellites being closer to the Earth’s surface, they are “brighter than the same satellites would be at higher orbital altitudes” and “more likely to exceed the unaided-eye brightness threshold if operators fail to design with this criterion in mind,” the report said. However, satellites “above 600km are an even greater concern to astronomers because they include all the impacts mentioned above, but can also be illuminated all night long. Full-night illumination causes these high-altitude constellations to impact a larger set of astronomical programs.”

Satellite constellations will be brightest “near the horizon and during twilight,” disproportionately impacting “searches for near-Earth objects (NEOs), distant Solar System objects and optical counterparts of fleeting gravitational wave sources,” the report said, adding:

Depending on constellation design, LEO satellites can also be visible deep into the night, broadening the impact to encompass all astronomical programs. We find that the worst-case constellation designs prove extremely impactful to the most severely affected science programs. For the less affected programs, the impact ranges from negligible to significant, requiring novel software and hardware efforts in an attempt to avoid satellites and remove trails from images.

Satellite constellations like OneWeb’s, with orbits of 1,200km, “present particularly serious challenges; they will be visible all night during summer and significant fractions of the night during winter, fall, and spring, and will have negative impacts on nearly all observational programs,” the report said. (OneWeb, which is going through a bankruptcy and sale, is also using medium-Earth orbits of 8,500km.)

So far, SpaceX has permission to launch nearly 12,000 satellites, OneWeb has approval for 2,000, and Amazon has approval for 3,236. SpaceX has applied to the Federal Communications Commission for another 30,000 satellites and OneWeb has applied for another 47,844.

Action plan

The report listed these methods of minimizing the impact on astronomy:

  1. Launch fewer or no LEOsat constellations. This is the only option identified that can achieve zero impact.
  2. Deploy satellites at orbital altitudes no higher than ~600 km.
  3. Darken satellites by lowering their albedo, shading reflected sunlight, or some combination thereof.
  4. Control each satellite’s attitude in orbit so that it reflects less sunlight to Earth.
  5. Remove or mask satellite trails and their effects in images.
  6. Avoid satellite trails with the use of accurate ephemerides [that provide data about a satellite’s position relative to Earth].

Satellite operators should also “make their best effort to avoid specular reflection (flares) in the direction of observatories.”

The report’s recommendations for observatories focus heavily on development of new software. Observatories should support “development of a software application available to the general astronomy community to identify, model, subtract, and mask satellite trails in images on the basis of user-supplied parameters,” the report said. They should also support development of observation-planning software for “the general astronomy community that predicts the time and projection of satellite transits through an image, given celestial position, time of night, exposure length, and field of view, based on the public database of ephemerides.”

Researchers also provided recommendations for work that observatories and satellite providers can do together, such as “an immediate coordinated effort for optical observations of LEOsat constellation members, to characterize both slowly and rapidly varying reflectivity and the effectiveness of experimental mitigations.”

There’s optimism about the ongoing collaboration. “I hope that the collegiality and spirit of partnership between astronomers and commercial satellite operators will expand to include more members of both communities and that it will continue to prove useful and productive,” NOIRLab director Patrick McCarthy said in a press release. “I also hope that the findings and recommendations in the SATCON1 report will serve as guidelines for observatories and satellite operators alike as we work towards a more detailed understanding of the impacts and mitigations and we learn to share the sky, one of nature’s priceless treasures.”

We’ve provided a summary of the report here, but if you want much more detail on the group’s findings and recommendations, you can check out the report and the lengthy appendices directly.

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Salty ponds found on Mars suggest stronger prospect of life on red planet, scientists say – CBC.ca

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A network of salty ponds may be gurgling beneath the South Pole on Mars, alongside a large underground lake, raising the prospect of tiny, swimming Martian life.

Italian scientists reported their findings Monday, two years after identifying what they believed to be a large buried lake. They widened their coverage area by a couple hundred miles, using even more data from a radar sounder on the European Space Agency’s Mars Express orbiter.

In the latest study appearing in the journal Nature Astronomy, the scientists provide further evidence of this salty underground lake, estimated to be 20 to 30 kilometres across and buried 1.5 kilometres beneath the icy surface.

Even more tantalizing, they’ve also identified three smaller bodies of water surrounding the lake. These ponds appear to be of various sizes and are separate from the main lake.

Roughly four billion years ago, Mars was warm and wet, like Earth. But the red planet eventually morphed into the barren, dry world it is today.

The research team led by Roma Tre University’s Sebastian Emanuel Lauro used a method similar to those used on Earth to detect buried lakes in the Antarctic and Canadian Arctic. They based their findings on more than 100 radar observations by Mars Express from 2010 to 2019; the spacecraft was launched in 2003.

All this potential water raises the possibility of microbial life on — or inside — Mars. High concentrations of salt are likely keeping the water from freezing at this frigid location, the scientists noted. The surface temperature at the South Pole is an estimated -113 degrees C and gets gradually warmer with depth.

These bodies of water are potentially interesting biologically and the researchers wrote that “future missions to Mars should target this region.” 

Earlier this year, a new computer model by NASA scientists lent further support to the theory that the ocean beneath the thick, icy crust of Jupiter’s moon Europa could be habitable.

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Salty lake, ponds may be gurgling beneath South Pole on Mars – CP24 Toronto's Breaking News

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Marcia Dunn, The Associated Press


Published Monday, September 28, 2020 7:46PM EDT

CAPE CANAVERAL, Fla. – A network of salty ponds may be gurgling beneath Mars’ South Pole alongside a large underground lake, raising the prospect of tiny, swimming Martian life.

Italian scientists reported their findings Monday, two years after identifying what they believed to be a large buried lake. They widened their coverage area by a couple hundred miles, using even more data from a radar sounder on the European Space Agency’s Mars Express orbiter.

In the latest study appearing in the journal Nature Astronomy, the scientists provide further evidence of this salty underground lake, estimated to be 12 miles to 18 miles (20 kilometres to 30 kilometres) across and buried 1 mile (1.5 kilometres) beneath the icy surface.

Even more tantalizing, they’ve also identified three smaller bodies of water surrounding the lake. These ponds appear to be of various sizes and are separate from the main lake.

Roughly 4 billion years ago, Mars was warm and wet, like Earth. But the red planet eventually morphed into the barren, dry world it remains today.

The research team led by Roma Tre University’s Sebastian Emanuel Lauro used a method similar to what’s been used on Earth to detect buried lakes in the Antarctic and Canadian Arctic. They based their findings on more than 100 radar observations by Mars Express from 2010 to 2019; the spacecraft was launched in 2003.

All this potential water raises the possibility of microbial life on – or inside – Mars. High concentrations of salt are likely keeping the water from freezing at this frigid location, the scientists noted. The surface temperature at the South Pole is an estimated minus 172 degrees Fahrenheit (minus 113 degrees Celsius), and gets gradually warmer with depth.

These bodies of water are potentially interesting biologically and “future missions to Mars should target this region,” the researchers wrote.

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Another look at possible under-ice lakes on Mars: They’re still there – Ars Technica

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In recent decades, we’ve become aware of lots of water on Earth that’s deep under ice. In some cases, we’ve watched this water nervously, as it’s deep underneath ice sheets, where it could lubricate the sheets’ slide into the sea. But we’ve also discovered lakes that have been trapped under ice near the poles, possibly for millions of years, raising the prospect that they could harbor ancient ecosystems.

Now, researchers are applying some of the same techniques that we’ve used to find those under-ice lakes to data from Mars. And the results support an earlier claim that there are bodies of water trapped under the polar ice of the red planet.

Spotting liquids from orbit

Mars clearly has extensive water locked away in the forum of ice, and some of it cycles through the atmosphere as orbital cycles make one pole or the other a bit warmer. But there’s not going to be pure liquid water on Mars—the temperatures just aren’t high enough for very long, and the atmospheric pressures are far too low to keep any liquid water from boiling off into the atmosphere.

Calculations suggest, however, that liquid water is possible on Mars—just not on the surface. With enough dissolved salts, a water-rich brine could remain liquid at the temperatures prevalent on Mars—even in the polar areas. And if it’s trapped under the Martian surface, there might be enough pressure to keep it liquid despite the thin atmosphere. That surface could be Martian soil, and people are thinking about that possibility. But the surface could also be one of the ice sheets we’ve spotted on Mars.

That possibility helped motivate the design of the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on the Mars Express orbiter. MARSIS is a radar device that uses wavelengths that water ice is transparent to. As a result, most of the photons that come back to the instrument are reflected by the interface between ice and something else: the atmosphere, the underlying bedrock, and potentially any interface between the ice and a liquid brine underneath it.

And that’s what the original results, published in 2018, seemed to indicate. In an area called Ultimi Scopuli near Mars’ south pole. The researchers saw a bright reflection, distinct from the one caused by the underlying bedrock, at some specific locations under the ice. And they interpreted this as indicating a boundary between ice and some liquid brines.

Now with more data

Two things have changed since those earlier results were done. One is that Mars Express has continued to pass over Mars’ polar regions, generating even more data for analysis. The second is that studies of ice-covered lakes on Earth have also advanced, with new ones identified from orbit using similar data. So some of the team behind the original work decided it was time to revisit the ice sheets at Ultimi Scopuli.

The analysis involves looking at details of the photons reflected back to the MARSIS instrument from a 250 x 300 square kilometer area. One aspect of that is the basic reflectivity of the different layers that can be discerned from the data. Other aspects of the signal can tell us about how smooth the surface of the reflective boundaries are and whether the nature of the boundary changes suddenly.

For example, the transition from an ice-bedrock boundary to an ice-brine one would cause a sudden shift from a relatively weak, uneven signal to a brighter and smoother one.

The researchers generated separate maps of the intensity and the smoothness of the signal and found that the maps largely overlapped, giving them confidence that they were identifying real transitions in the surfaces. A separate measure of the material (called permittivity) showed that it was high in the same location.

Overall, the researchers found that the largest area that’s likely to have water under the ice as about 20 by 30 kilometers. And it’s separated by bedrock features from a number of similar but smaller bodies. Calling these bodies “lakes” is speculative, given that we have no idea how deep they are. But the data certainly is consistent with some sort of under-ice feature—even if we use the standards of detection that have been used for under-ice lakes on Earth.

How did that get there?

The obvious question following the assumption that these bodies are filled with a watery brine is how that much liquid ended up there. We know that these salty solutions can stay liquid at temperatures far below the freezing point. But the conditions on Mars are such that most of minimum temperatures for water to remain liquid are right at the edge of the possible conditions at the site of the polar ice sheets. So some people have suggested geological activity as a possible source of heat to keep things liquid.

That’s not necessarily as unlikely as it may sound. Some groups have proposed that some features indicate that there was magma on the surface of Mars as recently as recently as 2 million years ago. But the researchers here argue that if things are on the edge of working under current climate conditions, there’s no need to resort to anything exceptional.

Instead, they suggest that the sorts of salts we already know are present on Mars can absorb water vapor out of the thin Martian atmosphere. Once formed, these can remain liquid down to 150 Kelvin, when the local temperatures at Ultimi Scopuli are likely to be in the area of 160 Kelvin and increase with depth.

And if that’s true, there could be liquid in many more locations at Mars’ poles. Not all of them are as amenable to orbital imaging as Ultimi Scopuli, but it’s a safe bet that this team will try to find additional ones.

Nature Astronomy, 2020. DOI: 10.1038/s41550-020-1200-6 (About DOIs).

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