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Shrinking Planets May Explain Why Hot Super-earths Exist

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vanishing gas giant

This artist’s concept shows giant clouds of hydrogen (blue) evaporating from the Neptune-sized exoplanet GJ 3470b as energetic charged particles from its host star beat down on the planet. The hydrogen is escaping the planet about 100 times faster than seen for any other similar alien world. (Credit: NASA/ESA/D. Player (STScI))

Astronomers have discovered a bizarre, Neptune-sized exoplanet located less than 100 light-years from Earth that’s shedding its atmosphere so quickly it may help researchers finally answer the long-standing question: Where did all the hot Neptunes go?

According to the new research, published December 13 in the journal Astronomy and Astrophysics, the shrinking world, named GJ 3470b, is rapidly losing its atmosphere as it’s bombarded by a steady stream of energetic charged particles from its red dwarf host.

The discovery — made with the help of NASA’s indefatigable Hubble Space Telescope — suggests that although Neptune-sized exoplanets can exist temporarily very near their host stars, they may not last very long. Instead, these planets could lose a significant fraction of their mass through evaporation driven by intense stellar winds. In the case of GJ 3470b, the researchers think strong winds from its active host star have stripped the planet of up to about 35 percent of its original mass over the course of its life.

“This is the first time a planet has been observed to lose its atmosphere so quickly that it can impact its evolution,” said lead author Vincent Bourrier, an astronomer from the University of Geneva (UNIGE), in a press release.

An Oasis in the Desert

Based on our own solar system, astronomers typically break down planets into three broad categories: rocky terrestrial planets (like Earth and Mars), massive gas giants (like Jupiter and Saturn), and freezing ice giants (like Uranus and Neptune). But over the years, researchers have discovered a multitude of exoplanets around other stars that seem to break these familiar molds.

In particular, since the first confirmed exoplanet was discovered just a few decades ago, researchers have uncovered a surprising number of giant planets, dubbed hot Jupiters, located extremely close to their host stars. On the other end of the spectrum, astronomers have discovered a plethora of hot super-Earths, which are a few times the mass of the Earth, that sit very near their stars. However, astronomers very rarely find medium-sized planets (or hot Neptunes) in similar close-in orbits.

But why does this void of hot, mid-sized planets — the so-called “hot Neptune desert” — exist?

hot neptune desert

This graphic plots known exoplanets based on both their size and their distance from their host stars. Hot Jupiters are in the upper left, while super-Earths are in the lower left. As shown, very few mid-size planets, or hot Neptunes, have been found orbiting very near their host stars. (For reference, the solar system’s innermost planet, Mercury, orbits the sun at an average distance of about 36 million miles.) (Credit: NASA/ESA/A. Feild (STScI))

“Until now, we were not sure of the role played by the evaporation of atmospheres in the formation of the desert,” said Bourrier. But based on this new finding, hot Neptunes may have withered away into mini-Neptunes (an alternative term for hefty super-Earths), or even eroded straight down to their rocky cores. “This could explain the abundance of hot super-Earths that have been discovered,” said co-author David Ehrenreich, an astronomer at UNIGE.

By showing that an active star can strip loads of mass from a mid-sized planet near the edge of the hot Neptune desert, the researchers think they’ve finally figured out why so few hot Neptunes have been discovered, while heaps of smaller planets, called super-Earths, have been found in the same boiling neighborhood.

“This is the smoking gun that planets can lose a significant fraction of their entire mass,” said co-author David Sing, a professor at Johns Hopkins University, in a statement. “GJ 3470b is losing more of its mass than any other planet we [have] seen so far; in only a few billion years from now, half of the planet may be gone.” And if GJ 3470b loses half its mass (it’s currently about 14 Earth masses), it will make the transition from hot Neptune to super-Earth.

Exploring the Desert

GJ 3470b, which sits about 10 times closer to its host star than Mercury is to the sun, is not the first evaporating Neptune-sized planet ever found. In fact, just a few years ago, astronomers found a similar planet named GJ 436b that is losing its atmosphere just like GJ3470b, albeit at a much slower rate (about 100 times slower). To analyze the mass loss of both these planets, the researchers tracked the hydrogen that was escaping from their atmospheres.

However, astronomers cannot easily detect hydrogen from more than about 150 light-years away. This is because the hydrogen signals they are looking for fall in a wavelength range that is blocked by interstellar gas, which permeates the space between stars. But fortunately, the researchers have a plan to seek out more distant shrinking hot Neptunes in the future.

“Helium will expand the range of our surveys,” said Bourrier, “the high sensitivity of the James Webb Space Telescope should allow us to detect helium escaping small planets, such as mini-Neptunes, and complete our observations of the edge of the desert.”

So, for now, we’ll have to be satisfied with just a few known examples of shrinking hot Neptunes. But keep in mind, many more may lurk just beyond the horizon.

 

[This article originally appeared on Astronomy.com]

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Ecology

Today’s letters: ‘Visionary’ plans don’t always work in Ottawa

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The opinion piece written by Tobi Nussbaum, CEO of the NCC, declares that a “bold, visionary transit plan” would showcase the capital.

As a long-term resident of Ottawa, I’ve had it with visionary plans. In the 1950s, the streetcars serving Ottawa so well were sent to the scrapyards. In the early ’60s, Queensway construction bulldozed established neighbourhoods and ripped the city apart. Later in the decade, the downtown railway station, which could have formed the hub of a commuter network, was relocated to the suburbs. These actions, in the name of “progress,” were undertaken with the “vision” to make Ottawa a car-reliant city.

Now we have an LRT, built just in time for most people to realize that they do not have to go downtown as they can work from home.

Current thinking is pushing a new “link” between Ottawa and Gatineau, with yet more expensive and disruptive infrastructure projects being touted, including a tramway or another tunnel under the downtown core.

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Ecology

That was then: Biggest earthquake since 1653 rocked Ottawa in 1925

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A regular weekly look-back at some offbeat or interesting stories that have appeared in the Ottawa Citizen over its 175-year history. Today: The big one hits.

The Ottawa Senators were playing a Saturday night game against the Montreal Canadiens at the Auditorium, the score tied 0-0 halfway through the second period. Sens’ rookie Ed Gorman and the Habs’ Billy Boucher had just served penalties for a dustup when the building began to make “ominous creaking sounds.” A window crashed to the ground.

Nearby, at Lisgar Collegiate, all eyes were on teenager Roxie Carrier, in the role of Donna Cyrilla in the musical comedy El Bandido. She had the stage to herself and was singing “Sometime” when the building rocked, the spotlight went out, and someone in the audience yelled “Fire!”

At a home on Carey Avenue, one woman’s normally relaxed cat suddenly arched its back, rushed around the room two or three times, spitting angrily, and climbed up the front-window curtains.

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Ecology

Ottawa delays small nuclear reactor plan as critics decry push for new reactors

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TORONTO — Canadians will have to wait a little while longer to see the federal government’s plan for the development of small nuclear reactors, seen by proponents as critical to the country’s fight against global warming.

Speaking at the opening of a two-day virtual international conference on Wednesday, the parliamentary secretary to the minister of natural resources said the plan will lay out key actions regarding the reactors. Its launch, Paul Lefebvre said, would come in the next few weeks.

“We’re still putting the finishing touches on it,” Lefebvre said. “The action plan is too important to be rushed.”

Small modular reactors — SMRs — are smaller in size and energy output than traditional nuclear power units, and more flexible in their deployment. While conventional reactors produce around 800 megawatts of power, SMRs can deliver up to 300 megawatts.

Proponents consider them ideal as both part of the regular electricity grid as well as for use in remote locations, including industrial sites and isolated northern communities. They could also play a role in the production of hydrogen and local heating.

“SMRs will allow us to take a bold step of meeting our goal of net-zero (emissions) by 2050 while creating good, middle class jobs and strengthening our competitive advantage,” said Lefebvre.

Natural Resources Minister Seamus O’Regan had been scheduled to speak at the conference but did not due to a family emergency.

Industry critics were quick to pounce on the government’s expected SMR announcement. They called on Ottawa to halt its plans to fund the experimental technology.

While nuclear power generation produces no greenhouse gas emissions, a major problem facing the industry is its growing mound of radioactive waste. This week, the government embarked on a round of consultations about what do with the dangerous material.

Dozens of groups, including the NDP, Bloc Quebecois, Green Party and some Indigenous organizations, oppose the plan for developing small modular reactors. They want the government to fight climate change by investing more in renewable energy and energy efficiency.

“We have options that are cheaper and safer and will be available quicker,” Richard Cannings, the NDP natural resources critic, said in a statement.

Lefebvre, however, said the global market for SMRs is expected to be worth between $150 billion and $300 billion a year by 2040. As one of the world’s largest producers of uranium, Canada has to be part of the wave both for economic and environmental reasons, he said.

“There’s a growing demand for smaller, simpler and affordable nuclear technology energy,” Lefebvre said.

Joe McBrearty, head of Canadian Nuclear Laboratories, told the conference the company had signed a host agreement this week with Ottawa-based Global First Power for a demonstration SMR at its Chalk River campus in eastern Ontario. A demonstration reactor will allow for the assessment of the technology’s overall viability, he said.

“When talking about deploying a new technology like an SMR, building a demonstration unit is vital to the success of that process,” McBrearty said. “Most importantly, it allows the public to see the reactor, to kick the tires so to speak, and to have confidence in the safety of its operation.”

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