** What’s Up: April 2020 Skywatching Tips from NASA – NASA JPL
What are some astronomy highlights in the sky in April 2020? This month, Venus visits the Pleiades; Mars, Jupiter and Saturn begin their breakup; and we ask, “What is the Moon illusion?” Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/whats-up…
Clear April nights are filled with starry creatures. Near the Big Dipper, you will find several interesting binary stars. You can also spot galaxies like the Pinwheel Galaxy, M82, and M96—the last of which is an asymmetric galaxy that may have been gravitationally disrupted by encounters with its neighbors. Keep watching for space-based views of these celestial objects.
Researchers using ESO’s Very Large Telescope (VLT) have observed an extreme planet where they suspect it rains iron. The ultra-hot giant exoplanet has a day side where temperatures climb above 2400 degrees Celsius, high enough to vaporise metals. Strong winds carry iron vapour to the cooler night side where it condenses into iron droplets.
“One could say that this planet gets rainy in the evening, except it rains iron,”
says David Ehrenreich, a professor at the University of Geneva in Switzerland. He led a study, published today in the journal Nature, of this exotic exoplanet. Known as WASP-76b, it is located some 390 light-years away in the constellation of Pisces.
This strange phenomenon happens because the ‘iron rain’ planet only ever shows one face, its day side, to its parent star, its cooler night side remaining in perpetual darkness. Like the Moon on its orbit around the Earth, WASP-76b is ‘tidally locked’: it takes as long to rotate around its axis as it does to go around the star.
On its day side, it receives thousands of times more radiation from its parent star than the Earth does from the Sun. It’s so hot that molecules separate into atoms, and metals like iron evaporate into the atmosphere. The extreme temperature difference between the day and night sides results in vigorous winds that bring the iron vapour from the ultra-hot day side to the cooler night side, where temperatures decrease to around 1500 degrees Celsius.
Not only does WASP-76b have different day-night temperatures, it also has distinct day-night chemistry, according to the new study. Using the new ESPRESSO instrument on ESO’s VLT in the Chilean Atacama Desert, the astronomers identified for the first time chemical variations on an ultra-hot gas giant planet. They detected a strong signature of iron vapour at the evening border that separates the planet’s day side from its night side.
“Surprisingly, however, we do not see the iron vapour in the morning,”
says Ehrenreich. The reason, he says, is that
“it is raining iron on the night side of this extreme exoplanet.”
[María Rosa Zapatero Osorio, an astrophysicist at the Centre for Astrobiology in Madrid, Spain, and the chair of the ESPRESSO science team, adds,]
“The observations show that iron vapour is abundant in the atmosphere of the hot day side of WASP-76b“
“A fraction of this iron is injected into the night side owing to the planet’s rotation and atmospheric winds. There, the iron encounters much cooler environments, condenses and rains down.“
This result was obtained from the very first science observations done with ESPRESSO, in September 2018, by the scientific consortium who built the instrument: a team from Portugal, Italy, Switzerland, Spain and ESO.
In March, the stars of spring lie eastward: Look for the constellations Gemini and Cancer to spot interesting celestial features like star clusters M35 and the Beehive Cluster, and NGC 3923, an oblong elliptical galaxy with an interesting ripple pattern. Keep watching for space-based views of the galaxies.
an apparent meeting or passing of two or more celestial bodies. The Moon is in conjunction with the Sun at the phase of New Moon, when it moves between the Earth and Sun and the side turned toward the Earth is dark. Inferior planets—those with orbits smaller than the Earth’s (namely, Venus and Mercury)—have two kinds of conjunctions with the Sun. An inferior conjunction occurs when the planet passes approximately between Earth and Sun; if it passes exactly between them, moving across the Sun’s face as seen from Earth, it is said to be in transit. A superior conjunction occurs when Earth and the other planet are on opposite sides of the Sun, but all three bodies are again nearly in a straight line. Superior planets, those having orbits larger than the Earth’s, can have only superior conjunctions with the Sun.
** Superb Stargazing *** Let’s Take a Trip to the Brightest Stars *** March 1-5 2020 – nemesis maturity
Let’s take a trip to the stars, constellations, planets and Moon, and discover the amazing wonders of the night sky. Let the Moon guide you to the brightest stars of the night sky over the next several evenings. Happy New Month and Happy Skywatching!
** [ Update March.2.2020: What’s Up: March 2020 Skywatching Tips from NASA
Looking for astronomy highlights for March 2020? This month, early risers enjoy a planetary grouping of Mars, Jupiter and Saturn in the early morning sky. Plus a closer look at Sirius, the brightest star in the sky, and spot a lovely trio at sunset on March 28. Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/whats-up… .
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, have spotted a peculiar gas cloud that resulted from a confrontation between two stars. One star grew so large it engulfed the other which, in turn, spiralled towards its partner provoking it into shedding its outer layers.
Like humans, stars change with age and ultimately die. For the Sun and stars like it, this change will take it through a phase where, having burned all the hydrogen in its core, it swells up into a large and bright red-giant star. Eventually, the dying Sun will lose its outer layers, leaving behind its core: a hot and dense star called a white dwarf.
“The star system HD101584 is special in the sense that this ‘death process’ was terminated prematurely and dramatically as a nearby low-mass companion star was engulfed by the giant,”
said Hans Olofsson of the Chalmers University of Technology, Sweden, who led a recent study, published in Astronomy & Astrophysics, of this intriguing object.
Thanks to new observations with ALMA, complemented by data from the ESO-operated Atacama Pathfinder EXperiment (APEX), Olofsson and his team now know that what happened in the double-star system HD101584 was akin to a stellar fight. As the main star puffed up into a red giant, it grew large enough to swallow its lower-mass partner. In response, the smaller star spiralled in towards the giant’s core but didn’t collide with it. Rather, this manoeuvre triggered the larger star into an outburst, leaving its gas layers dramatically scattered and its core exposed.
The team says the complex structure of the gas in the HD101584 nebula is due to the smaller star’s spiralling towards the red giant, as well as to the jets of gas that formed in this process. As a deadly blow to the already defeated gas layers, these jets blasted through the previously ejected material, forming the rings of gas and the bright bluish and reddish blobs seen in the nebula.
A silver lining of a stellar fight is that it helps astronomers to better understand the final evolution of stars like the Sun.
“Currently, we can describe the death processes common to many Sun-like stars, but we cannot explain why or exactly how they happen. HD101584 gives us important clues to solve this puzzle since it is currently in a short transitional phase between better studied evolutionary stages. With detailed images of the environment of HD101584 we can make the connection between the giant star it was before, and the stellar remnant it will soon become,”
says co-author Sofia Ramstedt from Uppsala University, Sweden.
Co-author Elizabeth Humphreys from ESO in Chile highlighted that ALMA and APEX, located in the country’s Atacama region, were crucial to enabling the team to probe “both the physics and chemistry in action” in the gas cloud. She added:
“This stunning image of the circumstellar environment of HD101584 would not have been possible without the exquisite sensitivity and angular resolution provided by ALMA.”
While current telescopes allow astronomers to study the gas around the binary, the two stars at the centre of the complex nebula are too close together and too far away to be resolved. ESO’s Extremely Large Telescope, under construction in Chile’s Atacama Desert,
“will provide information on the ‘heart’ of the object,”
says Olofsson, allowing astronomers a closer look at the fighting pair.