專門尋找系外行星的 Kepler 任務最終發現的行星總數約略落在了 3,000 顆左右，但想必這當中免不了會有一些「誤判」的行星存在的。MIT 的研究專家就發現 Kepler-699b、Kepler-840b 以及 Kepler-854b 這三顆「行星」質量都在木星的 2~4 倍之間，不太可能還是行星，更有可能是低質量的小恆星了。…
NASA’s James Webb Space Telescope passes key optics tests
Astronomers can breathe a little easier. NASA has confirmed the James Webb Space Telescope has passed checks and tests verifying its optical performance following a “fine phasing” alignment on March 11th. There also aren’t any critical problems or detectable blockages. Optical systems are performing “at, or above, expectations,” NASA said.
The fine phasing corrected alignment errors by using optical elements inside the James Webb Space Telescope’s NIRCam science instrument. The mission team gauged the performance by aligning and focusing the telescope on a star. The technology is very sensitive — as you can see above, Webb captured galaxies and stars in the background despite the very bright star in the middle.
NASA expects to finish aligning the observatory across all instruments by early May or sooner. After that, the team will spend two months prepping the instruments for capturing and sharing the first practical images and data in the summer.
The milestones show not just that Webb survived the 930,000-mile journey to its observation point, but that the telescope’s novel segmented mirror design works as promised — particularly important given the $10 billion price tag, numerous delays and Hubble’s mounting problems. For the most part, scientists can now concentrate on how they’ll use Webb to study the early universe and other elusive aspects of the cosmos.
Heliophysics pioneer Eugene Parker dies at 94
Dr. Eugene Parker, a pioneer in the field of heliophysics, has died at the age of 94. In the 1950s, Parker developed a theory that predicted solar winds. As NASA notes, Parker pushed the field forward throughout his career, “advancing ideas that addressed the fundamental questions about the workings of our Sun and stars throughout the universe.”
Heliophysics centers on the physics of the Sun and its impact on the Solar System. In 2018, NASA launched the Parker Solar Probe, the first spacecraft it named after a living person. The probe is tasked with observing the outer corona (or atmosphere) of the Sun to improve our understanding of solar winds and space weather. In December, it became the first spacecraft to enter the Sun’s upper atmosphere.
“Anyone who knew Dr. Parker, knew that he was a visionary. I was honored to stand with him at the launch of Parker Solar Probe and have loved getting to share with him all the exciting science results, seeing his face light up with every new image and data plot I showed him,” Nicola Fox, director of NASA’s heliophysics division, said. “I will sincerely miss his excitement and love for Parker Solar Probe. Even though Dr. Parker is no longer with us, his discoveries and legacy will live forever.”
Three ‘known’ Kepler exoplanets are more likely to be stars
The hunt for exoplanets has apparently led to a few near misses. MIT researchers have discovered that three “planets” observed using the Kepler Space Telescope (Kepler-699b, Kepler-840b and Kepler-854b) are more likely to be small stars. They’re simply too big, the scientists found — at two to four times Jupiter’s size, they’re larger than the largest confirmed planets.
A fourth, Kepler-747b, might also be ruled out. It’s small enough (‘just’ 1.8 times Jupiter’s size) to be a planet, but it’s distant enough that it doesn’t receive enough light to be sustainable. It’s “not entirely implausible” that 747b is a planet, according to MIT, but you won’t want to make any bets.
The team found the discrepancies after obtaining improved measurements from the European Space Agency’s Gaia observatory and double-checking the original classifications. Astronomers were only looking for tidal distortion at first, but noticed odd ellipsoidal signals (the ellipsoid shapes that hint at gravitational pull) that were too large for planets.
MIT doesn’t expect many more false planets. This is a “tiny correction,” the school’s Avi Shporer said. As it stands, this refinement is just what the scientists want — it produces more reliable data that should help with other, broader exoplanet studies.
UAE’s Hope probe tracked a massive dust storm across Mars
When the United Arab Emirates launched the Arab world’s first-ever mission to Mars in the summer of 2020, its desire was that its Hope probe would help provide scientists with a better understanding of the Red Planet’s weather systems. And it’s now done exactly that. According to The National, the probe recently spent two weeks tracking a massive dust storm across the surface of Mars.
Hope began following the weather event on December 29th. The probe entered the orbit of Mars equipped with a high-resolution camera and an infrared spectrometer. It used those tools to track the geographic distribution of dust, water vapor and carbon dioxide ice clouds displaced by the raging storm. Its orbital position allowed Hope to observe any variance in those elements in timescales measured in minutes and days, a feat previous missions to Mars didn’t have the ability to do.
What it saw was how quickly a storm can spread across the red planet. In the span of a single week, the storm it was tracking grew to stretch across more than 1,550 miles of Martian surface. In the process, it completely obscured geographic landmarks like the Hellas impact crater and sent dust haze as far as 2,485 miles away from the origin point of the storm. In addition to providing a play-by-play of a Martian storm, scientists hope the data Hope collected will allow them to gain a better understanding of how those storms can help water escape the planet’s atmosphere.
Hitting the Books: How Mildred Dresselhaus’ research proved we had graphite all wrong
Mildred Dresselhaus’ life was one in defiance of odds. Growing up poor in the Bronx — and even more to her detriment, growing up a woman in the 1940s — Dresselhaus’ traditional career options were paltry. Instead, she rose to become one of the world’s preeminent experts in carbon science as well as the first female Institute Professor at MIT, where she spent 57 years of her career. She collaborated with physics luminaries like Enrico Fermi and laid the essential groundwork for future Nobel Prize winning research, directed the Office of Science at the U.S. Department of Energy and was herself awarded the National Medal of Science.
In the excerpt below from Carbon Queen: The Remarkable Life of Nanoscience Pioneer Mildred Dresselhaus, author and Deputy Editorial Director at MIT News, Maia Weinstock, tells of the time that Dresselhaus collaborated with Iranian American physicist Ali Javan to investigate exactly how charge carriers — ie electrons — move about within a graphite matrix, research that would completely overturn the field’s understanding of how these subatomic particles operate.
MIT Press
Excerpted from Carbon Queen: The Remarkable Life of Nanoscience Pioneer Mildred Dresselhaus by Maia Weinstock. Reprinted with permission from The MIT Press. Copyright 2022.
A CRITICAL ABOUT-FACE
For anyone with a research career as long and as accomplished as that of Mildred S. Dresselhaus, there are bound to be certain papers that might get a bit lost in the corridors of the mind—papers that make only moderate strides, perhaps, or that involve relatively little effort or input (when, for example, being a minor consulting author on a paper with many coauthors). Conversely, there are always standout papers that one can never forget—for their scientific impact, for coinciding with particularly memorable periods of one’s career, or for simply being unique or beastly experiments.
Millie’s first major research publication after becoming a permanent member of the MIT faculty fell into the standout category. It was one she described time and again in recollections of her career, noting it as “an interesting story for history of science.”
The story begins with a collaboration between Millie and Iranian American physicist Ali Javan. Born in Iran to Azerbaijani parents, Javan was a talented scientist and award-winning engineer who had become well known for his invention of the gas laser. His helium-neon laser, coinvented with William Bennett Jr. when both were at Bell Labs, was an advance that made possible many of the late twentieth century’s most important technologies—from CD and DVD players to bar-code scanning systems to modern fiber optics.
After publishing a couple of papers describing her early magneto-optics research on the electronic structure of graphite, Millie was looking to delve even deeper, and Javan wanted to help. The two met during Millie’s work at Lincoln Lab; she was a huge fan, once calling him “a genius” and “an extremely creative and brilliant scientist.”
For her new work, Millie aimed to study the magnetic energy levels in graphite’s valence and conduction bands. To do this, she, Javan, and a graduate student, Paul Schroeder, employed a neon gas laser, which would provide a sharp point of light to probe their graphite samples. The laser had to be built especially for the experiment, and it took years for the fruits of their labor to mature; indeed, Millie moved from Lincoln to MIT in the middle of the work.
If the experiment had yielded only humdrum results, in line with everything the team had already known, it still would have been a path-breaking exercise because it was one of the first in which scientists used a laser to study the behavior of electrons in a magnetic field. But the results were not humdrum at all. Three years after Millie and her collaborators began their experiment, they discovered their data were telling them something that seemed impossible: the energy level spacing within graphite’s valence and conduction bands were totally off from what they expected. As Millie explained to a rapt audience at MIT two decades later, this meant that “the band structure that everybody had been using up till that point could certainly not be right, and had to be turned upside down.”
In other words, Millie and her colleagues were about to overturn a well-established scientific rule—one of the more exciting and important types of scientific discoveries one can make. Just like the landmark 1957 publication led by Chien-Shiung Wu, who overturned a long-accepted particle physics concept known as conservation of parity, upending established science requires a high degree of precision—and confidence in one’s results. Millie and her team had both.
What their data suggested was that the previously accepted placement of entities known as charge carriers within graphite’s electronic structure was actually backward. Charge carriers, which allow energy to flow through a conducting material such as graphite, are essentially just what their name suggests: something that can carry an electric charge. They are also critical for the functioning of electronic devices powered by a flow of energy.
Electrons are a well-known charge carrier; these subatomic bits carry a negative charge as they move around. Another type of charge carrier can be seen when an electron moves from one atom to another within a crystal lattice, creating something of an empty space that also carries a charge—one that’s equal in magnitude to the electron but opposite in charge. In what is essentially a lack of electrons, these positive charge carriers are known as holes.
MIT Press
FIGURE 6.1 In this simplified diagram, electrons (black dots) surround atomic nuclei in a crystal lattice. In some circumstances, electrons can break free from the lattice, leaving an empty spot or hole with a positive charge. Both electrons and holes can move about, affecting electrical conduction within the material.
Millie, Javan, and Schroeder discovered that scientists were using the wrong assignment of holes and electrons within the previously accepted structure of graphite: they found electrons where holes should be and vice versa. “This was pretty crazy,” Millie stated in a 2001 oral history interview. “We found that everything that had been done on the electronic structure of graphite up until that point was reversed.”
As with many other discoveries overturning conventional wisdom, acceptance of the revelation was not immediate. First, the journal to which Millie and her collaborators submitted their paper originally refused to publish it. In retelling the story, Millie often noted that one of the referees, her friend and colleague Joel McClure, privately revealed himself as a reviewer in hopes of convincing her that she was embarrassingly off-base. “He said,” Millie recalled in a 2001 interview, “‘Millie, you don’t want to publish this. We know where the electrons and holes are; how could you say that they’re backwards?’” But like all good scientists, Millie and her colleagues had checked and rechecked their results numerous times and were confident in their accuracy. And so, Millie thanked McClure and told him they were convinced they were right. “We wanted to publish, and we… would take the risk of ruining our careers,” Millie recounted in 1987.
Giving their colleagues the benefit of the doubt, McClure and the other peer reviewers approved publication of the paper despite conclusions that flew in the face of graphite’s established structure. Then a funny thing happened: bolstered by seeing these conclusions in print, other researchers emerged with previously collected data that made sense only in light of a reversed assignment of electrons and holes. “There was a whole flood of publications that supported our discovery that couldn’t be explained before,” Millie said in 2001.
Today, those who study the electronic structure of graphite do so with the understanding of charge carrier placement gleaned by Millie, Ali Javan, and Paul Schroeder (who ended up with quite a remarkable thesis based on the group’s results). For Millie, who published the work in her first year on the MIT faculty, the experiment quickly solidified her standing as an exceptional Institute researcher. While many of her most noteworthy contributions to science were yet to come, this early discovery was one she would remain proud of for the rest of her life.
俄羅斯拒絕發射剩餘的 OneWeb 網路衛星
俄國太空單位 Roscosmos 向 OneWeb 下了通牒，表示除非俄國能獲得保證 OneWeb 系統不會被用於戰爭中，且英國政府要完全退出 OneWeb 的股份，否則將不再替 OneWeb 發射衛星。