MIT aerospace engineers have found that greenhouse gas emissions are changing the environment of near-Earth space in ways that, over time, will reduce the number of satellites that can sustainably operate there.

In a study appearing today in Nature Sustainability, the researchers report that carbon dioxide and other greenhouse gases can cause the upper atmosphere to shrink. An atmospheric layer of special interest is the thermosphere, where the International Space Station and most satellites orbit today. When the thermosphere contracts, the decreasing density reduces atmospheric drag — a force that pulls old satellites and other debris down to altitudes where they will encounter air molecules and burn up.

Less drag therefore means extended lifetimes for space junk, which will litter sought-after regions for decades and increase the potential for collisions in orbit.

The team carried out simulations of how carbon emissions affect the upper atmosphere and orbital dynamics, in order to estimate the “satellite carrying capacity” of low Earth orbit. These simulations predict that by the year 2100, the carrying capacity of the most popular regions could be reduced by 50-66 percent due to the effects of greenhouse gases.

“Our behavior with greenhouse gases here on Earth over the past 100 years is having an effect on how we operate satellites over the next 100 years,” says study author Richard Linares, associate professor in MIT’s Department of Aeronautics and Astronautics (AeroAstro).

“The upper atmosphere is in a fragile state as climate change disrupts the status quo,” adds lead author William Parker, a graduate student in AeroAstro. “At the same time, there’s been a massive increase in the number of satellites launched, especially for delivering broadband internet from space. If we don’t manage this activity carefully and work to reduce our emissions, space could become too crowded, leading to more collisions and debris.”

The study includes co-author Matthew Brown of the University of Birmingham.

Sky fall

The thermosphere naturally contracts and expands every 11 years in response to the sun’s regular activity cycle. When the sun’s activity is low, the Earth receives less radiation, and its outermost atmosphere temporarily cools and contracts before expanding again during solar maximum.

In the 1990s, scientists wondered what response the thermosphere might have to greenhouse gases. Their preliminary modeling showed that, while the gases trap heat in the lower atmosphere, where we experience global warming and weather, the same gases radiate heat at much higher altitudes, effectively cooling the thermosphere. With this cooling, the researchers predicted that the thermosphere should shrink, reducing atmospheric density at high altitudes.

In the last decade, scientists have been able to measure changes in drag on satellites, which has provided some evidence that the thermosphere is contracting in response to something more than the sun’s natural, 11-year cycle.

“The sky is quite literally falling — just at a rate that’s on the scale of decades,” Parker says. “And we can see this by how the drag on our satellites is changing.”

The MIT team wondered how that response will affect the number of satellites that can safely operate in Earth’s orbit. Today, there are over 10,000 satellites drifting through low Earth orbit, which describes the region of space up to 1,200 miles (2,000 kilometers), from Earth’s surface. These satellites deliver essential services, including internet, communications, navigation, weather forecasting, and banking. The satellite population has ballooned in recent years, requiring operators to perform regular collision-avoidance maneuvers to keep safe. Any collisions that do occur can generate debris that remains in orbit for decades or centuries, increasing the chance for follow-on collisions with satellites, both old and new.

“More satellites have been launched in the last five years than in the preceding 60 years combined,” Parker says. “One of key things we’re trying to understand is whether the path we’re on today is sustainable.”

Crowded shells

In their new study, the researchers simulated different greenhouse gas emissions scenarios over the next century to investigate impacts on atmospheric density and drag. For each “shell,” or altitude range of interest, they then modeled the orbital dynamics and the risk of satellite collisions based on the number of objects within the shell. They used this approach to identify each shell’s “carrying capacity” — a term that is typically used in studies of ecology to describe the number of individuals that an ecosystem can support.

“We’re taking that carrying capacity idea and translating it to this space sustainability problem, to understand how many satellites low Earth orbit can sustain,” Parker explains.

The team compared several scenarios: one in which greenhouse gas concentrations remain at their level from the year 2000 and others where emissions change according to the Intergovernmental Panel on Climate Change (IPCC) Shared Socioeconomic Pathways (SSPs). They found that scenarios with continuing increases in emissions would lead to a significantly reduced carrying capacity throughout low Earth orbit.

In particular, the team estimates that by the end of this century, the number of satellites safely accommodated within the altitudes of 200 and 1,000 kilometers could be reduced by 50 to 66 percent compared with a scenario in which emissions remain at year-2000 levels. If satellite capacity is exceeded, even in a local region, the researchers predict that the region will experience a “runaway instability,” or a cascade of collisions that would create so much debris that satellites could no longer safely operate there.

Their predictions forecast out to the year 2100, but the team says that certain shells in the atmosphere today are already crowding up with satellites, particularly from recent “megaconstellations” such as SpaceX’s Starlink, which comprises fleets of thousands of small internet satellites.

“The megaconstellation is a new trend, and we’re showing that because of climate change, we’re going to have a reduced capacity in orbit,” Linares says. “And in local regions, we’re close to approaching this capacity value today.”

“We rely on the atmosphere to clean up our debris. If the atmosphere is changing, then the debris environment will change too,” Parker adds. “We show the long-term outlook on orbital debris is critically dependent on curbing our greenhouse gas emissions.”

This research is supported, in part, by the U.S. National Science Foundation, the U.S. Air Force, and the U.K. Natural Environment Research Council.

The malware includes four separate backdoors:

Creating four backdoors facilitates the attackers having multiple points of re-entry should one be detected and removed. A unique case we haven’t seen before. Which introduces another type of attack made possibly by abusing websites that don’t monitor 3rd party dependencies in the browser of their users.

The four backdoors:

The functions of the four backdoors are explained below:

• Backdoor 1, which uploads and installs a fake plugin named “Ultra SEO Processor,” which is then used to execute attacker-issued commands ...

A new federal report downplaying or denying climate change could drive a reversal of climate rules and expansion of executive authority.

It continues President Donald Trump's move to walk away from global climate agreements.

The lawsuit represents the latest salvo in a battle with the Trump administration over the agency's Greenhouse Gas Reduction Fund.

The state will remain out of the regional carbon-trading program, pending appeal of a finding that the state's withdrawal was illegal.

Analysis shows the oil giant sharply increased its use of carbon credits to offset its emissions as the voluntary market faced criticism.

Twelve years ago, the states agreed to collectively promote electric vehicles. Supporters say their success shows the power of state-level rules and incentives.

A proposal to delay rules aimed at boosting electric truck sales is the latest sign of Democratic lawmakers’ growing discomfort over implementing a landmark climate law.

The council said Switzerland “had failed to comply with its duties” to combat climate change and meet emissions targets.

A member of the European Parliament argued that “the program provides insufficient financial control and accountability" for nongovernmental organizations.

“Butterflies have been declining the last 20 years,” a study co-author said. “And we don't see any sign that that’s going to end.”

Last month saw digital rights organizations and social justice groups head to Taiwan for this year's RightsCon conference on human rights in the digital age. During the conference, one prominent message was spoken loud and clear: Alaa Abd El-Fattah must be immediately released from illegal detention in Egypt.

"As Alaa’s mother, I thank you for your solidarity and ask you to not to give up until Alaa is out of prison."

During the RightsCon opening ceremony, Access Now’s Executive Director, Alejandro Mayoral Baños, affirmed the urgency of Alaa’s situation in detention and called for Alaa’s freedom. The RightsCon community was also addressed by Alaa’s mother, mathematician Laila Soueif, who has been on hunger strike in London for 158 days. In a video highlighting Alaa’s work with digital rights and his role in this community, she stated: “As Alaa’s mother, I thank you for your solidarity and ask you to not to give up until Alaa is out of prison.” Laila was admitted to hospital the next day with dangerously low blood sugar, blood pressure and sodium levels.

RightsCon participants gather in solidarity with the #FreeAlaa campaign

The calls to #FreeAlaa and save Laila were again reaffirmed during the closing ceremony in a keynote by Sara Alsherif, Migrant Digital Justice Programme Manager at Open Rights Group and close friend of Alaa. Referencing Alaa’s early work as a digital activist, Alsherif said: “He understood that the fight for digital rights is at the core of the struggle for human rights and democracy.” She closed by reminding the hundreds-strong audience that “Alaa could be any one of us … Please do for him what you would want us to do for you if you were in his position.”

During RightsCon, with Laila still in hospital, calls for UK Prime Minister Starmer to get on the phone with Egyptian President Sisi reached a fever pitch, and on 28 February, one day after the closing ceremony, the UK government issued a press release affirming that Alaa’s case had been discussed, with Starmer pressing for Alaa’s freedom. 

Alaa should have been released on September 29, after serving a five-year sentence for sharing a Facebook post about a death in police custody, but Egyptian authorities have continued his imprisonment in contravention of the country’s own Criminal Procedure Code. British consular officials are prevented from visiting him in prison because the Egyptian government refuses to recognise Alaa’s British citizenship.

Laila Soueif has been on hunger strike for more than five months while she and the rest of his family have worked in concert with various advocacy groups to engage the British government in securing Alaa’s release. On December 12, she also started protesting daily outside the Foreign Office and has since been joined by numerous MPs and public figures. Laila still remains in hospital, but following Starmer’s call with Sisi agreed to take glucose, she stated that she is ready to end her hunger strike if progress is made. 

Laila Soueif and family meeting with UK Prime Minister Keir Starmer

As of March 6, Laila has moved to a partial hunger strike of 300 calories per day citing “hope that Alaa’s case might move.” However, the family has learned that Alaa himself began a hunger strike on March 1 in prison after hearing that his mother had been hospitalized. Laila has said that without fast movement on Alaa’s case she will return to a total hunger strike. Alaa’s sister Sanaa, who was previously jailed by the regime on bogus charges, visited Alaa on March 8.

If you’re based in the UK, we encourage you to write to your MP to urgently advocate for Alaa’s release (external link): https://freealaa.net/message-mp 

Supporters everywhere can share Alaa’s plight and Laila’s story on social media using the hashtags #FreeAlaa and #SaveLaila. Additionally, the campaign’s website (external link) offers additional actions, including purchasing Alaa’s book, and participating in a one-day solidarity hunger strike. You can also sign up for campaign updates by e-mail.

Every second counts, and time is running out. Keir Starmer and the British government must do everything it can to ensure Alaa’s immediate and unconditional release.

Tuberculosis lives and thrives in the lungs. When the bacteria that cause the disease are coughed into the air, they are thrust into a comparatively hostile environment, with drastic changes to their surrounding pH and chemistry. How these bacteria survive their airborne journey is key to their persistence, but very little is known about how they protect themselves as they waft from one host to the next.

Now MIT researchers and their collaborators have discovered a family of genes that becomes essential for survival specifically when the pathogen is exposed to the air, likely protecting the bacterium during its flight.

Many of these genes were previously considered to be nonessential, as they didn’t seem to have any effect on the bacteria’s role in causing disease when injected into a host. The new work suggests that these genes are indeed essential, though for transmission rather than proliferation.

“There is a blind spot that we have toward airborne transmission, in terms of how a pathogen can survive these sudden changes as it circulates in the air,” says Lydia Bourouiba, who is the head of the Fluid Dynamics of Disease Transmission Laboratory, an associate professor of civil and environmental engineering and mechanical engineering, and a core faculty member in the Instiute for Medical Engineering and Science at MIT. “Now we have a sense, through these genes, of what tools tuberculosis uses to protect itself.”

The team’s results, appearing this week in the Proceedings of the National Academy of Sciences, could provide new targets for tuberculosis therapies that simultaneously treat infection and prevent transmission.

“If a drug were to target the product of these same genes, it could effectively treat an individual, and even before that person is cured, it could keep the infection from spreading to others,” says Carl Nathan, chair of the Department of Microbiology and Immunology and R.A. Rees Pritchett Professor of Microbiology at Weill Cornell Medicine.

Nathan and Bourouiba are co-senior authors of the study, which includes MIT co-authors and mentees of Bourouiba in the Fluids and Health Network: co-lead author postdoc Xiaoyi Hu, postdoc Eric Shen, and student mentees Robin Jahn and Luc Geurts. The study also includes collaborators from Weill Cornell Medicine, the University of California at San Diego, Rockefeller University, Hackensack Meridian Health, and the University of Washington.

Pathogen’s perspective

Tuberculosis is a respiratory disease caused by Mycobacterium tuberculosis, a bacterium that most commonly affects the lungs and is transmitted through droplets that an infected individual expels into the air, often through coughing or sneezing. Tuberculosis is the single leading cause of death from infection, except during the major global pandemics caused by viruses.

“In the last 100 years, we have had the 1918 influenza, the 1981 HIV AIDS epidemic, and the 2019 SARS Cov2 pandemic,” Nathan notes. “Each of those viruses has killed an enormous number of people. And as they have settled down, we are left with a ‘permanent pandemic’ of tuberculosis.”

Much of the research on tuberculosis centers on its pathophysiology — the mechanisms by which the bacteria take over and infect a host — as well as ways to diagnose and treat the disease. For their new study, Nathan and Bourouiba focused on transmission of tuberculosis, from the perspective of the bacterium itself, to investigate what defenses it might rely on to help it survive its airborne transmission.

“This is one of the first attempts to look at tuberculosis from the airborne perspective, in terms of what is happening to the organism, at the level of being protected from these sudden changes and very harsh biophysical conditions,” Bourouiba says.

Critical defense

At MIT, Bourouiba studies the physics of fluids and the ways in which droplet dynamics can spread particles and pathogens. She teamed up with Nathan, who studies tuberculosis, and the genes that the bacteria rely on throughout their life cycle.

To get a handle on how tuberculosis can survive in the air, the team aimed to mimic the conditions that the bacterium experiences during transmission. The researchers first looked to develop a fluid that is similar in viscosity and droplet sizes to what a patient would cough or sneeze out into the air. Bourouiba notes that much of the experimental work that has been done on tuberculosis in the past has been based on a liquid solution that scientists use to grow the bacteria. But the team found that this liquid has a chemical composition that is very different from the fluid that tuberculosis patients actually cough and sneeze into the air.

Additionally, Bourouiba notes that fluid commonly sampled from tuberculosis patients is based on sputum that a patient spits out, for instance for a diagnostic test. “The fluid is thick and gooey and it’s what most of the tuberculosis world considers to represent what is happening in the body,” she says. “But it’s extraordinarily inefficient in spreading to others because it’s too sticky to break into inhalable droplets.”

Through Bourouiba’s work with fluid and droplet physics, the team determined the more realistic viscosity and likely size distribution of tuberculosis-carrying microdroplets that would be transmitted through the air. The team also characterized the droplet compositions, based on analyses of patient samples of infected lung tissues. They then created a more realistic fluid, with a composition, viscosity, surface tension and droplet size that is similar to what would be released into the air from exhalations.

Then, the researchers deposited different fluid mixtures onto plates in tiny individual droplets and measured in detail how they evaporate and what internal structure they leave behind. They observed that the new fluid tended to shield the bacteria at the center of the droplet as the droplet evaporated, compared to conventional fluids where bacteria tended to be more exposed to the air. The more realistic fluid was also capable of retaining more water.

Additionally, the team infused each droplet with bacteria containing genes with various knockdowns, to see whether the absence of certain genes would affect the bacteria’s survival as the droplets evaporated.

In this way, the team assessed the activity of over 4,000 tuberculosis genes and discovered a family of several hundred genes that seemed to become important specifically as the bacteria adapted to airborne conditions. Many of these genes are involved in repairing damage to oxidized proteins, such as proteins that have been exposed to air. Other activated genes have to do with destroying damaged proteins that are beyond repair.

“What we turned up was a candidate list that’s very long,” Nathan says. “There are hundreds of genes, some more prominently implicated than others, that may be critically involved in helping tuberculosis survive its transmission phase.”

The team acknowledges the experiments are not a complete analog of the bacteria’s biophysical transmission. In reality, tuberculosis is carried in droplets that fly through the air, evaporating as they go. In order to carry out their genetic analyses, the team had to work with droplets sitting on a plate. Under these constraints, they mimicked the droplet transmission as best they could, by setting the plates in an extremely dry chamber to accelerate the droplets’ evaporation, analogous to what they would experience in flight.

Going forward, the researchers have started experimenting with platforms that allow them to study the droplets in flight, in a range of conditions. They plan to focus on the new family of genes in even more realistic experiments, to confirm whether the genes do indeed shield Mycobacterium tuberculosis as it is transmitted through the air, potentially opening the way to weakening its airborne defenses.

“The idea of waiting to find someone with tuberculosis, then treating and curing them, is a totally inefficient way to stop the pandemic,” Nathan says. “Most people who exhale tuberculosis do not yet have a diagnosis. So we have to interrupt its transmission. And how do you do that, if you don’t know anything about the process itself? We have some ideas now.”

This work was supported, in part, by the National Institutes of Health, the Abby and Howard P. Milstein Program in Chemical Biology and Translational Medicine, and the Potts Memorial Foundation, the National Science Foundation Center for Analysis and Prediction of Pandemic Expansion (APPEX), Inditex, NASA Translational Research Institute for Space Health , and Analog Devices, Inc.

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Energy-economic models are increasingly being used to inform climate mitigation policies. This Comment describes three situations where models misinform policymakers and calls for more iterative, policy-orientated modelling exercises that maximize learning in the pursuit of long-term emissions reductions goals.