Recent claims of potential biosignatures on the exoplanet K2-18b have been challenged by researchers at the University of Chicago. Their analysis suggests that the detection of dimethyl sulfide may be inconclusive due to overlapping signals from non-biological molecules, emphasizing the limitations of current detection technology and urging caution against premature conclusions.
Astronomers have discovered the first evidence of magnetic worlds beyond the solar system thanks to their high-speed, violent winds, representing a major step forward in exoplanet research.
Astronomers have discovered the first evidence of magnetic worlds beyond the solar system thanks to their high-speed, violent winds, representing a major step forward in exoplanet research.
NASA’s Parker Solar Probe captured the first visible light images of Venus from space. The images, taken during two recent flybys, show a faint glow from the surface, revealing features like continents, plains, and plateaus. The images could help scientists learn about Venus’s geology and mineral make-up and understand why it became inhospitable while Earth […]
Researchers have uncovered an unexpected phenomenon, dubbed the Zwan-Wolf effect, squeezing plasma "like toothpaste" in Mars' upper atmosphere. This effect, which also happens on Earth, was thought to be impossible on the Red Planet.
The planet’s name is HD 189733b. It is one of the closest extrasolar planets to Earth that can be studied in detail, and one of the most thoroughly characterised exoplanets in the astronomical literature. Its star, HD 189733, sits in the constellation Vulpecula, the Little Fox, north of the celestial equator. The star itself is faintly visible to a small telescope from any dark backyard in the northern hemisphere on a clear summer night. The planet is not. The planet has never been directly photographed and probably never will be by any current generation of telescope.
Everything that is known about it has been deduced from the way its star’s light changes as the planet passes in front of, alongside, and behind it. The deductions, after twenty years of accumulated work, describe one of the most hostile environments in the catalogued universe.
It was discovered on 5 October 2005 by François Bouchy and colleagues at the Haute-Provence Observatory in southern France, using the Doppler-spectroscopy method to detect the small gravitational tug of the planet on its host star. The planet is approximately the mass and size of Jupiter. It sits roughly 4.6 million kilometres from its star, which is about one-thirtieth of the distance between the Sun and Mercury. It completes one orbit every 2.2 Earth days. At that distance, it is tidally locked. The same hemisphere faces the star at all times.
On the side facing the star, it is approximately 1,000 degrees Celsius.
What it would be like to be there
The astronomers who have studied HD 189733b in detail describe an atmosphere that has no analogue in the solar system. The temperature differential between the planet’s permanently lit day side and its permanently dark night side, measured by NASA’s Spitzer Space Telescope in 2007, is approximately 260 degrees Celsius. That differential drives atmospheric winds at speeds that, in the upper atmosphere on the day side, reach approximately 7,000 kilometres per hour. As the European Space Agency set out in its 2013 announcement of the planet’s confirmed colour, the wind speeds are roughly seven times the speed of sound. On Earth, by comparison, the strongest sustained surface winds ever recorded reached approximately 410 kilometres per hour during a tropical cyclone. HD 189733b’s winds are approximately seventeen times faster.
The atmosphere is composed primarily of hydrogen and helium, like Jupiter’s, but it also contains a high concentration of silicate particles. Silicates are the family of minerals that make up most of the Earth’s crust, including sand, quartz, and the basaltic rocks that form ocean floors. On HD 189733b, at atmospheric temperatures exceeding 1,000 degrees Celsius, silicate particles condense in the atmosphere from gaseous form into small molten droplets of glass.
The droplets do not fall straight down. They are driven sideways by the 7,000 km/h winds, at velocities at which a single droplet impacting a surface would carry the energy of a small artillery shell. The planet, on the side facing its star, is therefore experiencing continuous horizontal precipitation of molten glass at hurricane speeds, at temperatures that would melt aluminium.
The rain is the weather. There is no break in it.
How they figured out it was blue
The visual colour of an exoplanet 63 light-years away cannot be observed in the conventional sense. The planet is far too faint and far too close to its star to be photographed directly. The team that established HD 189733b’s true colour, led by Tom Evans at the University of Oxford, used a technique called secondary eclipse spectroscopy. Their paper, published in Astrophysical Journal Letters on 1 August 2013, describes the method in detail.
The Hubble Space Telescope’s Space Telescope Imaging Spectrograph observed the HD 189733 system continuously through several full orbital cycles of the planet. During each orbit, the planet passes behind the star from the telescope’s perspective. In the moments before and after the planet disappears behind the star, the telescope is receiving light from both the star and the planet. In the moments when the planet is hidden, the telescope is receiving light from the star alone. By subtracting the second measurement from the first, the team could isolate the light reflected by the planet alone.
The drop in brightness as the planet vanished behind its star was measurable specifically in the blue part of the spectrum, between 290 and 450 nanometres. The drop in the red and near-infrared was much smaller. The published interpretation is that the planet reflects blue light at approximately three to four times the rate it reflects red light, which makes it, in the visual range, a deep cobalt blue.
If a human observer could be positioned in space within the HD 189733 system, at a safe distance, the planet would appear to them as a small, deep blue point of light, almost indistinguishable in colour from the way the Earth appears to astronauts looking back from the International Space Station.
The mechanism that produces the blue colour, however, is completely different.
What the blue actually is
Earth appears blue from space for two reasons. The most obvious is the reflection of light from the oceans, which cover approximately 71 per cent of the planet’s surface. The second, less commonly understood, is Rayleigh scattering in the atmosphere. Short-wavelength light, including blue, scatters more efficiently off the molecules of nitrogen and oxygen in the air than long-wavelength light does. This is why the sky is blue. The same effect contributes to the planet’s blue appearance from orbit.
HD 189733b has no oceans and probably no liquid water of any kind. The temperatures are too high for water to exist as a liquid anywhere in the atmosphere. The blue colour comes entirely from the silicate particles. The droplets of molten glass suspended and condensing in the atmosphere scatter blue light preferentially, in much the same way that nitrogen and oxygen molecules in Earth’s atmosphere scatter blue light. The mechanism is a different kind of Rayleigh-like scattering, off particles that are themselves molten and being driven sideways by hurricane-speed winds, but the optical outcome is similar.
HD 189733b is, by the resemblance of one colour to another, a kind of cosmic mimicry. A planet that looks, from sixty-three light-years away, like Earth. A planet that, on inspection, has nothing in common with Earth except the wavelength of the light it reflects.
Why it matters
HD 189733b belongs to a class of exoplanets called hot Jupiters: gas giants similar in mass and composition to Jupiter, orbiting their stars at distances much closer than Mercury orbits the Sun. The first hot Jupiter was discovered in 1995. Since then, several hundred have been confirmed in the published exoplanet catalogue maintained by NASA’s Exoplanet Exploration Program. They are, on the data so far, surprisingly common in the galaxy. They are also, on the same data, completely absent from our own solar system.
The reasons hot Jupiters form, and the processes that drive them inward to such close orbits around their stars, are still subjects of active investigation. HD 189733b, because of its relative closeness to Earth and its bright host star, has become one of the most-studied hot Jupiters in the astronomical literature. The 2013 confirmation of its blue colour was the first time the visible-light colour of any exoplanet had been measured directly. The same observational programme, and follow-ups using the James Webb Space Telescope, have detected water vapour, carbon dioxide, methane, and atmospheric haze in the planet’s upper layers, building up a picture of an atmosphere chemically rich and physically violent at scales no observation of a solar-system planet has matched.
The exoplanet has, in the years since its discovery, been informally referred to in the astronomical literature as the planet where it rains glass. The wind speeds, the temperatures, and the silicate atmospheric chemistry are now well established. The geological details — whether the molten glass droplets reach the planet’s deeper layers as glass or evaporate back into vapour, whether the planet has a coherent solid core or whether its interior is a continuous fluid down to whatever pressure ultimately produces metallic hydrogen — remain open questions.
What 63 light-years actually means
The light that the Hubble Space Telescope captured in 2013 had been travelling toward Earth since approximately 1950. The light Hubble might capture from HD 189733b today began its journey toward us during the early 1960s. The planet itself, in real time, is doing whatever it has continued to do for the four billion years it has existed. The astronomers who study it are studying its past.
If a human civilisation around HD 189733 were, at this moment, observing Earth through the same kind of telescope Hubble represents, they would be looking at images of Earth as it was in 1962. They would be receiving the light Earth was reflecting during the Cuban Missile Crisis, the early Mercury space programme, and the year before the death of John F. Kennedy.
Earth, from sixty-three light-years away, also looks like a deep blue dot.
The difference is that ours, on closer inspection, has oceans.
How do you weigh a planet you can't see? Astronomers may have the answer and it involves "reading between the rings," the bright beautiful structures exoplanets create.
How do you weigh a planet you can't see? Astronomers may have the answer and it involves "reading between the rings," the bright beautiful structures exoplanets create.
Earth has many unique features for a planet, such as a magnetic field, a large moon, and plate tectonics. It’s also the only planet we know of that harbors life. These facts form the basis of the Rare Earth hypothesis, which posits that we haven’t found aliens because other planets in the Galaxy probably don’t have all the right conditions for life.
Another characteristic of Earth is that about 30% of its surface is land and about 70% is ocean. Recently, Columbia University Assistant Professor David Kipping investigated whether the proportion of Earth’s surface covered by dry land versus ocean, or its land fraction, is another reason Earth is habitable not only for simple single-celled organisms, but also for intelligent species like humans.
To test this hypothesis, Kipping created 4 statistical models of planets with different land fractions that intelligent aliens could potentially evolve on. First, he created an equation to describe the likelihood that a planet in its star’s habitable zone has a particular land fraction, known as a probability distribution. Kipping weighted this probability distribution toward the extreme ends, making it more likely that a planet would be covered by a single huge landmass or a single vast ocean than by a mix of both, as on Earth.
Kipping then incorporated this land fraction probability distribution into his statistical models to calculate the probability that a random planet will have that land fraction and host intelligent life. The 4 scenarios Kipping tested were: 1) that intelligent life is more likely to emerge on land-dominated planets, 2) that it’s more likely to emerge on ocean-dominated planets, 3) that it’s more likely to emerge on planets with roughly equal amounts of land and ocean, and 4) that its emergence is independent of a planet’s land fraction.
As a first step in determining the kinds of planets intelligent aliens would tend to emerge on, Kipping used each model to predict the probability that intelligent life would emerge on a planet with the same land fraction as Earth. He then compared these probabilities by calculating the ratios between each value. Because Earth is the only known planet with intelligent life, a model that predicted a greater probability for humanity’s existence on Earth would be more likely to reflect reality.
Kipping considered it strong evidence that a given model was more realistic than another if the ratio between 2 of them was greater than 10, meaning one model was 10 times more likely to predict the existence of Earth and humanity. Kipping found that no comparison of any 2 models passed this threshold. However, the models assuming that intelligent life prefers ocean-dominated planets or planets with a land-ocean balance were 2.5 and 3 times more likely to predict the existence of humanity than the model assuming that intelligent life prefers land-dominated planets. Additionally, the model assuming that intelligent life prefers a land-ocean balance was always more likely to predict humanity than any other model, though marginally.
Kipping also addressed whether finding more planets with intelligent life would affect which model was deemed most realistic, for example, if scientists discovered conclusive evidence of life on Mars in its distant past. Here, Kipping identified 2 complications. First, it’s uncertain how much of Mars’s surface was once covered by water – some estimate it had a land fraction as high as 81%, while others estimate it was as low as 25%. Second, proving that Mars once had life would not prove it once had intelligent life.
Regardless, Kipping reran the models assuming that ancient Mars had a land fraction comparable to Earth’s. Adding this second data point produced ratios similar to those in the earlier Earth-only calculations, meaning it still didn’t make any single model 10 times more likely to predict the existence of humans and Martians, respectively.
Kipping then took the 10-times threshold and reversed the calculations to find what conditions would exceed it. In doing so, he calculated that astronomers would need to find 14 other planets with intelligent life and known land fractions to robustly determine whether intelligent life is more likely to occur on desert planets, ocean planets, balanced planets, or without bias.
Kipping concluded that he can’t yet definitively state whether there is something special about Earth’s land fraction when it comes to producing intelligent species. However, Earth’s existence would suggest that intelligent life is unlikely to favor extreme desert planets, so the Milky Way probably isn’t filled with Tatooines and Jakkus. And while his analysis doesn’t debunk the Rare Earth hypothesis, it does undermine the argument that Earth’s ocean size explains why Earth is rare.
Models suggest that impact-ejected material from Earth could reach Venus’ clouds and potentially survive there briefly. Panspermia is the idea that life, or the ingredients needed for life, can move through space on asteroids, comets, and other objects. If life’s building blocks appear on one planet, a powerful impact could blast material from its surface [...]
Researchers have uncovered an unexpected phenomenon, dubbed the Zwan-Wolf effect, squeezing plasma "like toothpaste" in Mars' upper atmosphere. This effect, which also happens on Earth, was thought to be impossible on the Red Planet.
The largest moon in the solar system — Jupiter’s Ganymede — has a unique and inexplicable magnetic field. New research could finally explain it: the moon is heating up.
Researchers have uncovered an unexpected phenomenon, dubbed the Zwan-Wolf effect, squeezing plasma "like toothpaste" in Mars' upper atmosphere. This effect, which also happens on Earth, was thought to be impossible on the Red Planet.
The largest moon in the solar system — Jupiter’s Ganymede — has a unique and inexplicable magnetic field. New research could finally explain it: the moon is heating up.
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Models suggest that impact-ejected material from Earth could reach Venus’ clouds and potentially survive there briefly. Panspermia is the idea that life, or the ingredients needed for life, can move through space on asteroids, comets, and other objects. If life’s building blocks appear on one planet, a powerful impact could blast material from its surface [...] 
