S27E66: BepiColombo's Glitch: Navigating Challenges on the Road to Mercury

[00:00:00] This is SpaceTime Series 27 Episode 66 for broadcast on the 31st of May 2024.

[00:00:07] Coming up on SpaceTime, a glitch aboard the BepiColombo spacecraft bound for Mercury,

[00:00:13] exploring the unexplored regions of Venus, and an explanation for stars that mysteriously

[00:00:20] suddenly vanish. All that and more coming up on SpaceTime.

[00:00:25] Welcome to SpaceTime with Stuart Gary

[00:00:45] The joint ESA-JAXA BepiColombo spacecraft has experienced a sudden glitch, which is

[00:00:50] preventing the probe's thrusters from operating at full power. BepiColombo is a three-part

[00:00:55] spacecraft consisting of two scientific probes and the Mercury Transfer Module. The three

[00:01:01] sections are designed to separate from each other as part of the mission's Mercury orbit

[00:01:06] operation. The solar arrays and electric propulsion system on the Mercury Transfer Module

[00:01:11] are used to generate thrust during the spacecraft's complex cruise phase from Earth to Mercury.

[00:01:17] However, as BepiColombo was scheduled to begin its next manoeuvre in late April,

[00:01:21] the Transfer Module failed to deliver enough energy to the spacecraft's ion thrusters.

[00:01:26] BepiColombo's flight control team working at ESA's Mission Control Centre in Darmstadt,

[00:01:31] Germany, were able to eventually restore about 90% of the spacecraft's thrust capabilities.

[00:01:37] However, the Transfer Module's available power is still less than it should be and so full thrust

[00:01:42] cannot yet be restored. Mission managers' current priorities are to maintain stable

[00:01:47] spacecraft propulsion at the current power level and to estimate how this will affect

[00:01:52] upcoming operations. Meanwhile, a second team are working to determine the root cause of the

[00:01:57] problem and to try and maximise the amount of electrical power available for the ion thrusters.

[00:02:02] Now if the current power levels can be maintained, BepiColombo should arrive at

[00:02:06] Mercury in time for its fourth Gravity Assist in September. The final orbit insertion at

[00:02:11] Mercury is slated for December 2025 and the start of routine science operations for early 2026.

[00:02:19] BepiColombo's array of scientific instruments are designed to study Mercury's composition,

[00:02:24] its atmosphere, its magnetosphere and its history and evolution, and to address

[00:02:29] long-standing questions about its formation and the evolution of the solar system.

[00:02:34] This report from ESA TV. A collaboration between ESA and the Japanese space agency JAXA,

[00:02:40] BepiColombo consists of two scientific orbiters, a Transfer Module to propel them to Mercury

[00:02:46] and a sunshield. Protected by hand-stitched ceramic thermal blankets, the entire spacecraft

[00:02:54] is 6.5 metres high. Designed to withstand temperatures of up to 450 degrees Celsius,

[00:02:59] BepiColombo is one of the most technically and scientifically complex missions ever launched.

[00:03:06] 80% of our material needs to be re-qualified for this mission because we hadn't tested before in

[00:03:14] that harsh environment. So it's a real challenge to go there and to bring two spacecraft

[00:03:20] in an orbit around Mercury. The first challenge is getting to Mercury. Flying directly isn't an

[00:03:26] option. The sun's gravity means any spacecraft would be going too fast to make it into orbit.

[00:03:32] Instead, BepiColombo will take seven years to reach its destination,

[00:03:37] combining solar electric propulsion with a total of nine flybys of Earth, Venus and Mercury.

[00:03:44] When we fly, we constantly brake against the sun because we fly into the inner side of our

[00:03:50] solar system. And when you fly towards the most heaviest element there, you constantly accelerate.

[00:03:57] We don't want that. That's why we decelerate. Once they arrive at Mercury in late 2025,

[00:04:04] the orbiters will separate from the transfer module to begin their comprehensive scientific

[00:04:09] mission in 2026. With its 11 instruments, ESA's Mercury Planetary Orbiter will study the surface

[00:04:17] and internal composition of the planet. Meanwhile, JAXA's Mercury Magnetospheric Orbiter's five

[00:04:24] instruments will study the planet's magnetic field. Together, the orbiters will not only reveal

[00:04:30] more about Mercury, but also the history of the inner solar system. Because Mercury is not

[00:04:36] tilted like Earth, it's spinning almost in the orbital plane. Therefore, there are some craters

[00:04:43] on the poles that never see sunlight. And in these craters, we found water ice. And this water

[00:04:50] ice could be stable over millions and billions of years. And that's a fantastic thing also about

[00:04:56] And in that report from ESA TV, we heard from BepiColombo Project Scientist Johannes Benckhoff

[00:05:02] from ESA and BepiColombo Project Manager Erlich Reinenhaus also from ESA.

[00:05:08] This is Space Time. Still to come, exploring the unexplored regions of Venus,

[00:05:14] and finally an explanation for stars that mysteriously suddenly vanish.

[00:05:19] All that and more still to come on Space Time.

[00:05:23] Now while we're on the subject of BepiColombo, a fleeting visit by the spacecraft to Venus has

[00:05:43] revealed surprising insights into how gases are stripped away from the upper layers of the

[00:05:48] planet's atmosphere. A report in the journal Nature Astronomy claims that observations in

[00:05:53] the previously unexplored region of Venus' magnetic environment show that carbon and

[00:05:58] oxygen are being accelerated to speeds where they can escape the planet's gravitational pull.

[00:06:03] It's the first time that positively charged carbon ions have been seen escaping from Venus'

[00:06:10] atmosphere. These are heavy ions that are usually slow moving, so astronomers are still trying to

[00:06:15] understand the mechanisms at play. It could be that an electrostatic wind is lifting them away

[00:06:20] from the planet, or they could be accelerated through centrifugal processes. Unlike Earth,

[00:06:25] Venus doesn't generate an intrinsic geomagnetic field in its core.

[00:06:30] Nonetheless, a weak comet-shaped induced magnetosphere is created around the planet

[00:06:35] simply by the interaction of charged particles emitted by the sun and the solar wind with

[00:06:39] electrically charged particles in Venus' upper atmosphere. Draped around the magnetosphere

[00:06:44] is a region called the magneto sheath where the solar wind is slowed and heated.

[00:06:50] Back on August 10th 2021, BepiColombo passed by Venus on a gravity assist maneuver designed to

[00:06:56] slow the spacecraft down and adjust its course towards its final destination of Mercury.

[00:07:01] In the process, the probe swooped through the long tail of Venus' magneto sheath and emerged

[00:07:06] through the nose of the magnetic regions closest to the sun. Over a 90-minute period of observations,

[00:07:13] BepiColombo's instruments measured the number and mass of charged particles it encountered,

[00:07:17] capturing information about the chemical and physical processes driving atmospheric escape

[00:07:22] in the flank of the magneto sheath. Early in its history, Venus had many similarities to the Earth,

[00:07:28] including significant amounts of liquid water. But interactions with the solar wind have stripped

[00:07:33] away the water, leaving an atmosphere composed mainly of carbon dioxide and smaller amounts of

[00:07:38] nitrogen and other trace gases. Previous missions, including NASA's Pioneer Venus Orbiter

[00:07:44] and ESA's Venus Express, have made detailed studies of the type and quantity of molecules

[00:07:49] and other charged particles that are being lost into space. However, the mission's orbital paths

[00:07:55] have left some areas around Venus unexplored and so many questions have remained unanswered.

[00:08:00] The data for this study were obtained by BepiColombo's Mass Spectrum Analyzer and its

[00:08:05] Mercury Ion Analyzer during the spacecraft's second Venus flyby. The two sensors are part of

[00:08:11] the Mercury Plasma Particle Experiment instrument package which is carried on the JAXA-led Mercury

[00:08:16] Magnetospheric Orbiter. Mass Spectrum Analyzer's principal investigator, Dominique Delcourt from

[00:08:22] the Plasma Physics Laboratory, says characterizing the loss of heavy ions and understanding the

[00:08:27] escape mechanisms at Venus is crucial to understand how the planet's atmosphere has evolved

[00:08:32] and how it's lost all its water. Europlanet spied at space weather modelling tools then

[00:08:38] enabled researchers to track how the particles would have propagated through the Venusian magneto sheath.

[00:08:44] Recent results suggest that the atmospheric escape from Venus cannot fully explain the loss

[00:08:49] of its historical water content. Over the next decade, a fleet of spacecraft will investigate

[00:08:55] Venus, including ESA's EnVision mission, NASA's Veritas Orbiter and Da Vinci probe, and India's

[00:09:01] Shukran orbiter. Collectively, the spacecraft will provide a comprehensive picture of the Venusian

[00:09:07] environment from the magneto sheath down through the atmosphere to the surface and interior.

[00:09:13] This is Space Time. Still to come, finally an explanation for stars that mysteriously suddenly

[00:09:20] vanish, and the June solstice, the spectacular Sombrero galaxy, the heart of our own galaxy,

[00:09:26] the constellation Sagittarius, and the Taurids' meteor shower are among the many highlights of

[00:09:32] the June night skies on Skywatch. Astronomers are showing new evidence of how massive stars

[00:09:53] can simply disappear, turning into stellar-mass black holes with a whisper rather than a scream.

[00:10:00] Known as complete stellar collapse, the mysterious phenomenon involves the sudden

[00:10:04] disappearance of a massive star without the usual supernova explosion. The star just appears to

[00:10:11] suddenly vanish from the night sky. See, usually when stars eight or more times the mass of our

[00:10:17] sun run out of the nuclear fuel needed to trigger fusion, the process that makes stars shine, they

[00:10:22] undergo core collapse, with the entire mass of the star crashing down onto the stellar core.

[00:10:28] This triggers a huge explosion called a supernova, which is bright enough to outshine an entire

[00:10:34] galaxy. What's left behind is usually a tiny super-dense object called a neutron star just

[00:10:40] a dozen or so kilometres across, but containing so much compacted mass a teaspoon of neutron star

[00:10:46] material would weigh billions of tons. Now alternatively, an even more massive star would

[00:10:52] collapse beyond the neutron star phase, becoming a stellar-mass black hole, an object of infinite

[00:10:58] density occupying zero volume. And gravity around such an extreme object is so intense nothing,

[00:11:04] not even light, can escape. The new research suggests that with enough mass, a star's

[00:11:10] gravitational pull can be so strong that during its core collapse process no supernova explosion

[00:11:16] takes place. Instead, the star goes through what's called a complete collapse. The study's

[00:11:22] lead author Alejandro Vigna-Gomez from the Niels Bohr Institute says the discovery is linked to

[00:11:27] the sudden disappearance of brightly shining stars which had interested astronomers for years.

[00:11:32] The study involved observations of an unusual binary star system called VFTS-243 located in

[00:11:39] the Large Magellanic Cloud, a dwarf galaxy orbiting the Milky Way. The VFTS-243 system

[00:11:46] comprises a large main sequence star and a black hole roughly 10 times the mass of our sun with

[00:11:51] the pair orbiting each other. Now astronomers know the system contains a black hole even though it

[00:11:56] can't be seen because of the way the main sequence stars orbiting with the black hole around a common

[00:12:01] centre of gravity. Normally evidence for supernovae such as a natal kick, gravitational perturbations,

[00:12:08] gas bubbles, irradiated space or debris clouds called supernova remnants can be identified and

[00:12:14] measured for centuries after the event. And also there's usually a neutron star at the heart of

[00:12:19] the remnant. But in the case of VFTS-243 there are no traces of a supernova. A natal kick involves

[00:12:27] the violent forces of a supernova directly affecting newborn neutron stars and black

[00:12:32] holes left by it because of the asymmetric emission of matter during the explosion.

[00:12:37] This kick causes the compact object to accelerate, pushing the neutron star up to 1000 km per second

[00:12:43] away from the location of the initial supernova event. The speed is expected to be less for

[00:12:48] stellar mass black holes but still significant. Because the black hole in the VFTS-243 system

[00:12:55] only appears to have been accelerated to roughly 4 km per second, it shows no signs of having

[00:13:00] received a substantial natal kick as would be expected had it undergone a supernova.

[00:13:05] Also, the symmetry of the star system's orbit usually shows some signs that it had felt the

[00:13:10] impact of a violent supernova explosion because of the ejection of material that happens.

[00:13:16] But instead, the researchers found symmetry in the orbit. The orbit of VFTS-243 is almost circular,

[00:13:23] indicating there are no signs of large asymmetries during collapse.

[00:13:27] So the analysis all points to the black hole being formed immediately in the initial core

[00:13:32] collapse, with the energy mainly being lost as neutrinos. The results highlight VFTS-243

[00:13:39] as the best observable case so far for the theory of stellar mass black holes being formed through

[00:13:45] total collapse. The VFTS-243 system opens the possibility for finally comparing a range of

[00:13:52] astrophysics theories and model calculations with actual observations. So undoubtedly,

[00:13:58] this star system will be incredibly important for studying stellar evolution and collapse.

[00:14:04] This is Space Time.

[00:14:22] Okay, time now to turn our eyes to the skies as we check out the celestial sphere for the

[00:14:26] month of June on Skywatch. June is the fourth month of the year in the old Roman calendar.

[00:14:32] It's named after Juno, who was the wife of Jupiter and is also the equivalent of the

[00:14:37] Greek goddess Hera. Another belief is that the month's name comes from the Latin word

[00:14:42] junoris, which means the younger ones. June also marks the winter solstice in the southern hemisphere,

[00:14:48] and of course it means the arrival of summer for our lucky listeners north of the equator,

[00:14:53] which this year happens at 6.50 in the morning of Friday, June 21, Australian Eastern Standard Time.

[00:14:59] That's 20.50 on the night of Thursday, June 20, Greenwich Mean Time, and 4.50 in the afternoon,

[00:15:05] US Eastern Daylight Time. The June solstice occurs when the sun reaches its most northerly

[00:15:11] point in the sky as seen from Earth, zenith appearing to be directly over the Tropic of Cancer.

[00:15:17] It all happens because the seasons are governed by the tilt of Earth's axis as it journeys around

[00:15:21] the sun every year. On the day of the June solstice, the Earth's south pole is tilted by 23.5

[00:15:28] degrees away from the sun, so the sun rises north of east and sets north of west. When the south

[00:15:34] pole is tilted towards the sun, it's the southern hemisphere's summer. Between these two, we have

[00:15:40] the autumn and spring equinox. Variations in temperatures on Earth aren't determined by the

[00:15:45] Earth's orbital distance from the sun, but rather the angle of the sun's rays striking the Earth.

[00:15:50] In the summer, the sun's high in the sky and the rays hit the Earth at a steep angle.

[00:15:55] But in winter, the sun's lower down in the sky and the rays strike the Earth at a more shallow

[00:16:00] angle. In most parts of the world, seasons begin on the day of the equinox and solstice.

[00:16:06] However, in Australia, seasons begin on the first day of a specific calendar month – March for

[00:16:12] autumn, June for winter, September for spring, and December for summer.

[00:16:17] Okay, let's turn to the constellations, and almost directly overhead this time of the year,

[00:16:21] we have the spectacular constellation Virgo. The constellation Virgo is named after Virgo,

[00:16:27] the goddess of justice and the harvest in ancient Greek mythology, who used her scales to weigh good

[00:16:32] and evil. However, she became so disenchanted with the deeds of evil men, she threw away her

[00:16:38] scales and retreated to the heavens. Interestingly, the ancient Egyptians also associated Virgo with

[00:16:44] agriculture. There, she was the goddess Isis, who sprinkled heads of wheat across the sky,

[00:16:50] forming the Milky Way. To science, Virgo is a tightly packed region of space containing some

[00:16:56] 2,000 galaxies, all gravitationally bound into a giant galaxy cluster located some 60 million

[00:17:02] light years away. Our own local group of galaxies, which is primarily bound by the Milky Way and

[00:17:09] Andromeda, are an outlying member of this cluster. The Virgo Cluster is the heart of the Virgo

[00:17:15] Supercluster, one of the largest known structures in the universe, a massive galactic node in the

[00:17:20] large-scale cosmic web-like structure of the universe. The mass of the Virgo Supercluster is

[00:17:26] so great that its gravity generates the Virgo-centric flow, causing our Milky Way galaxy,

[00:17:31] as well as Andromeda and all the other members of the local group, to move towards the supercluster

[00:17:36] at about 400 km per second. That's despite the accelerated expansion of the universe over

[00:17:42] cosmic timescales. The Virgo Supercluster is now thought in turn to be simply a lobe of an even

[00:17:48] bigger galaxy supercluster called Laniakea, the center of which is known as the Great Attractor.

[00:17:54] Despite the Virgo Cluster's size, it's so far away it's hard to see without a decently-sized

[00:18:00] backyard telescope. You'll need something at least 100 mm in diameter or larger.

[00:18:05] Directly overhead right now is the constellation Corvus the Crow. Greek mythology tells us that

[00:18:12] Corvus could talk to humans, but he was a lazy bird, and so Apollo took away his ability to speak

[00:18:18] and banished him to the heavens. One of the highlights in the constellations Virgo and Corvus

[00:18:23] is the spectacular Sombrero Galaxy M104. Visible with a good pair of binoculars or a small telescope,

[00:18:30] this stunning spiral galaxy is seen almost edge-on, providing audiences with a spectacular

[00:18:36] backlit view of its galactic bold stars and the molecular gas and dust lanes in its arms.

[00:18:43] M104 is located some 31 million light-years away, and it's moving away from our Milky Way galaxy

[00:18:49] at about 1,000 km per second. A light-year is 10 trillion km. The distance a photon can travel

[00:18:56] in a year at the speed of light, which is about 300,000 km per second in a vacuum and the ultimate

[00:19:02] speed limit of the universe. The Sombrero Galaxy has a diameter of about 50,000 light-years,

[00:19:09] about 30% the size of our Milky Way. It's surrounded by around 2,000 globular clusters

[00:19:15] and has an active central supermassive black hole at least a billion times the mass of the Sun.

[00:19:21] By comparison, Sagittarius A star, that's the supermassive black hole at the centre of our

[00:19:26] Milky Way galaxy, is just 4.3 million times the mass of the Sun. Globular clusters are tight

[00:19:32] stellar balls comprising millions to billions of stars, which were either the central remnants of

[00:19:38] a smaller galaxy cannibalised by a larger one, or they were originally all part of the same

[00:19:43] stellar nursery formed at the same time in the same collapsing molecular gas and dust cloud.

[00:19:49] The brightest star in the constellation Virgo is Spica, a spectroscopic binary located some 250

[00:19:55] light-years away. Spectroscopic binaries are pairs of stars so close to each other that they

[00:20:01] can only be separated using a spectrograph to determine the individual chemical makeup of each

[00:20:06] component. Looking about 20 degrees above the western horizon in the early evening this time

[00:20:11] of the year, you'll find the brightest star in the night sky, the Dog Star Sirius. Only the Sun,

[00:20:18] the Moon and the planet Venus look brighter. To the northwest or right of Sirius from the

[00:20:23] southern hemisphere is another fairly bright star called Procyon, the brightest star in Canis

[00:20:28] Minor, the lesser dog. In Greek mythology, Canis Major and Canis Minor were Orion's two hunting

[00:20:35] dogs. Procyon is another binary star system, this one comprising a spectral type F main-sequence

[00:20:41] white-yellow star, Procyon A, and a faint white dwarf companion, Procyon B. Main-sequence stars

[00:20:49] are those undergoing core hydrogen fusion into helium. Astronomers describe stars in terms of

[00:20:55] spectral types, a classification system based on temperature and characteristics. The hottest,

[00:21:01] the most massive, most luminous stars in the sky are known as spectral type O blue stars.

[00:21:07] They're followed by spectral type B blue-white stars, then spectral type A white stars,

[00:21:12] spectral type F white-yellowish stars, followed by spectral type G yellow stars, that's where our

[00:21:18] Sun fits in, then spectral type K orange stars and the coolest and least massive stars known

[00:21:24] are spectral type M red dwarf stars. Each spectral classification can further be subdivided using a

[00:21:30] numerical digit to represent temperature with zero being the hottest and nine the coolest.

[00:21:35] And then you can add a Roman numeral to represent luminosity. Now put that all together and our own

[00:21:41] local star of the Sun becomes a G2V or G25 yellow dwarf star. Also included in the stellar

[00:21:48] classification system are spectral types LT and Y, which are assigned to failed stars known as

[00:21:54] brown dwarfs, some of which were born as spectral type M red dwarf stars but became brown dwarfs

[00:22:00] after burning off some of their mass. Brown dwarfs fit into a category between the largest planets,

[00:22:05] which are around 13 times the mass of Jupiter, and the smallest spectral type M red dwarf stars,

[00:22:11] which are between 75 and 80 times the mass of Jupiter or 0.08 solar masses.

[00:22:18] White dwarfs are the stellar corpses of Sun-like stars. Having used up their nuclear fuel supply,

[00:22:24] fusing hydrogen into helium in their core, these stars expand into red giants as they begin fusing

[00:22:30] helium into carbon and oxygen. However, Sun-like stars aren't massive enough to fuse carbon and

[00:22:36] oxygen into heavier elements, and so they turn off. Their outer gaseous envelopes then float off into

[00:22:43] space as spectacular objects known as planetary nebulae. What's left behind is a super dense white

[00:22:49] hot stellar core about the size of the Earth, a white dwarf, which will slowly cool over the eons.

[00:22:57] The white dwarf Procyon B is about 0.6 times the mass of the Sun and has a diameter of around

[00:23:02] 8600 km. Located some 11.6 light years away, Procyon A has about one and a half times the

[00:23:10] mass and twice the radius of our Sun. Interestingly, Procyon A has about seven times the Sun's luminosity

[00:23:17] that makes it unusually bright for this type of star, and that suggests that it's starting to

[00:23:22] evolve off the main sequence after having fused nearly all of its core hydrogen into helium.

[00:23:27] It's expanding out to become a sub-giant as it begins fusing core helium into oxygen and carbon

[00:23:33] and burning hydrogen into helium in a shell around the core. As it continues to expand,

[00:23:39] the star will eventually swell to somewhere between 80 and 150 times its current diameter,

[00:23:45] becoming a bloated red or orange giant. That'll probably happen within the next 10 to 100 million

[00:23:51] years. The two stars, Procyon A and B, orbit each other every 40.82 Earth years at an average

[00:23:58] distance of 15 astronomical units. That's about the distance of Mercury's orbit around the Sun.

[00:24:04] An astronomical unit is the average distance between the Earth and the Sun,

[00:24:08] about 150 million kilometers or 8.3 light minutes. Looking to the north-northwest from

[00:24:14] the southern hemisphere this time of year, you'll see the constellation Leo the Lion,

[00:24:19] looking more like a bunch of stars shaped like an upside-down question mark.

[00:24:23] Located 36.7 light years away, Arcturus is a bloated aging red giant, about 7.1 billion years

[00:24:30] old and nearing the end of its life. Having used up all its core hydrogen, it's now fusing helium

[00:24:37] into carbon and oxygen. This has caused the star, which is only slightly more massive than our Sun,

[00:24:42] to expand out to around 25 times the Sun's diameter, becoming about 170 times as luminous.

[00:24:49] It'll soon puff off its outer gaseous envelope as a planetary nebulae, exposing its white-hot

[00:24:54] stellar core and becoming a white dwarf. In Greek mythology, Arcturus was the guardian of the bear.

[00:25:02] This is a reference to it being next to the constellations Ursa Major and Ursa Minor,

[00:25:06] the greater and lesser bears. There's some indication that Arcturus could have a binary

[00:25:11] stellar companion, but the results are inconclusive at this stage. There's also speculation that it

[00:25:17] could have a large planet or substellar object about 12 Jupiter masses orbiting it. That's

[00:25:22] close to brown dwarf size, but again the research remains inconclusive. To the east, when viewing

[00:25:27] from the southern hemisphere this time of year, are the three bright stars in the constellation

[00:25:32] Libra at the scales of Justice. They're visible about halfway, or about 40 degrees above the

[00:25:37] horizon. These also represent the claws of Scorpius the scorpion, which is chasing Orion across the

[00:25:44] sky. The brightest star in the constellation Scorpius is Alpha Scorpii or Antares, the

[00:25:50] scorpion's heart. Easily seen with the unaided eye, the red supergiant Antares is located some

[00:25:57] 550 light years away and it's one of the largest known stars in the universe. It has about 18 times

[00:26:04] the mass but 883 times the diameter of our Sun. Antares is also around 10 000 times more luminous

[00:26:12] than our Sun. Now looking to the southeast from the southern hemisphere and you'll see the

[00:26:16] constellation Sagittarius the archer. Sagittarius is important because it marks the direction

[00:26:22] towards the center of our Milky Way galaxy. In fact, located just 27 000 light years away in

[00:26:28] the direction of Sagittarius is the home of the galaxy's central supermassive black hole, Sagittarius A

[00:26:34] star. To the ancient Babylonians, Sagittarius was the god Nergal the centaur, a creature half man

[00:26:41] and half horse. By the time Greek mythology took over, Sagittarius was also carrying a bow loaded

[00:26:47] with an arrow pointing directly towards Antares at the heart of Scorpius the scorpion. The center

[00:26:53] of the Milky Way and its supermassive black hole Sagittarius A star lie in the westernmost part of

[00:26:59] Sagittarius. Sagittarius has many spectacular highlights. Alpha Sagittarii or Rookbat,

[00:27:06] meaning the archer's knee, is a spectrotype B blue star. Located some 182 light years away,

[00:27:12] it is two and a half times the diameter of the Sun and is about 40 times as luminous. Astronomers

[00:27:18] think it's surrounded by a dense debris disk and has a newborn companion star which is only just

[00:27:23] starting to join the main sequence. The brightest star in Sagittarius is Epsilon Sagittarii or Cal

[00:27:31] the southern part of the bow. Epsilon Sagittarii is a binary system located some 143 light years

[00:27:37] from Earth. The primary star is an evolved spectrotype B blue giant nearing the end of

[00:27:43] its life on the main sequence. It has about three and a half times the mass of the Sun, almost seven

[00:27:48] times the Sun's radius and is radiating around 363 times the Sun's luminosity. It's also a strong

[00:27:56] X-ray source and is spinning very rapidly with an estimated radial velocity of some 236 km per

[00:28:03] second. The system also displays an excess of infrared radiation emissions, suggesting the

[00:28:08] presence of a circumstellar disk of dust. The second star in the system appears to be inside

[00:28:14] this debris disk. Astronomers think it's going to be a spectrotype G yellow dwarf star with about 95%

[00:28:21] the mass of the Sun. Sigma Sagittarii or Nunki is the constellation's second brightest star.

[00:28:27] The name Nunki is Babylonian, however its meaning has been lost through the sands of time.

[00:28:32] It's thought to represent the ancient Babylonian sacred city of Erdu on the Euphrates River.

[00:28:38] If correct, that would make Nunki the oldest stellar name currently in use.

[00:28:43] It's another spectrotype B blue star located some 260 light years away.

[00:28:48] It has about 8 times the Sun's mass, about 4.5 times its radius and some 3,300 times the Sun's

[00:28:55] luminosity. Zeta Sagittarii or Acela the armpit is a binary star system located some 88 light years

[00:29:03] away and it's currently speeding away from our solar system. Astronomers think that it may have

[00:29:08] been as near as one and a half light years from the Sun around 1.4 million years ago. That would

[00:29:13] have made it an extremely close former neighbor. One of the stars in the system is a spectrotype A

[00:29:19] white giant while the other is a spectrotype A white supergiant, the pair orbiting each other

[00:29:24] every 21 Earth years. The system's combined mass is about 5.26 times the mass of the Sun.

[00:29:32] Delta Sagittarii or Calsmeridionalis appears to be a double star system located 348 light years away

[00:29:39] and listed as an orange giant. Then there's Eta Sagittarii, another double star system,

[00:29:44] this one located 146 light years from Earth. The primary star is an aging bloated red giant

[00:29:51] on the asymptotic giant branch. That means it's no longer fusing hydrogen or helium in its core

[00:29:56] and is instead fusing heavier elements in the core and burning hydrogen and helium in its shell.

[00:30:02] It's already expanded out to some 57 times the radius of the Sun and is now nearing the end of

[00:30:07] its life. The second star in the system is a spectrotype F main sequence white yellow dwarf

[00:30:14] which appears to be in a binary system with a primary star orbiting it every 1,270 Earth years.

[00:30:21] Pi Sagittarii or Albalda is a triple star system located around 510 light years away.

[00:30:27] The primary star appears to be another spectrotype F white yellow giant and it looks like it's just

[00:30:33] about exhausted its core hydrogen and is now moving off the main sequence and evolving into

[00:30:38] a red giant. Pi Sagittarii has two nearby companions but we know little about them.

[00:30:44] Beta Sagittarii or Arqab, the Achilles tendon, is the designation shared by two separate star

[00:30:49] systems, one around 378 light years from Earth, the other 379 light years away. Beta Sagittarii A

[00:30:57] is a spectrotype B blue dwarf star while Beta Sagittarii B is a white yellow giant.

[00:31:03] Lying near the very center of the constellation is Nova Sagittarii which was only discovered in

[00:31:07] 2015 and as the name suggests is a nova, a white dwarf in a binary system which is constantly

[00:31:14] drawing material off a close orbiting companion star. Once enough mass reaches the surface of

[00:31:19] the white dwarf, the added mass will undergo a thermonuclear explosion causing the star to

[00:31:25] briefly light up like a beacon and then slowly fade again over the following few weeks or months.

[00:31:31] The blast isn't enough to destroy the white dwarf, only the additional material it's picked up.

[00:31:36] Now once the star has gone nova and the additional mass has been burnt off,

[00:31:40] the same cycle starts over again and the process repeats itself on time scales ranging from every

[00:31:45] few years to tens of thousands of years. The Sagittarius constellation also hosts many

[00:31:51] star clusters and nebulae including some of the best known astronomical objects in the sky.

[00:31:57] These include the spectacular Lagoon Nebula Messier 8, a stunning pink emission nebula

[00:32:02] that's located 5,000 light years away and measures 140 light years by 60 light years across.

[00:32:09] The central area of the Lagoon Nebula is also known as the Hourglass Nebula. That's because

[00:32:14] of its distinctive shape because of matter propelled by a massive star forming region

[00:32:18] called Herschel 36. It's one of the few star forming nebulae possible to see with the unaided

[00:32:24] eye. The Lagoon Nebula was instrumental in the discovery of Bock Globules, more than 17,000 of

[00:32:30] which have now been found in the nebula. Astronomers believe these globules contain

[00:32:35] embryonic protostars destined to eventually become new stellar generations. Probably the most famous

[00:32:42] nebula in Sagittarius is Messier 17, better known as the Horsehead Nebula. It's located some

[00:32:48] 4,890 light years away in a dense region of ionized atomic hydrogen. Also known as the Omega

[00:32:55] or Swan Nebula, it spans some 15 light years in diameter and has some 800 times the mass of our

[00:33:01] Sun. It's considered one of the brightest and most massive star forming regions in our galaxy

[00:33:06] with a geometry similar to the Orion Nebula except that we're seeing it edge on rather than face on.

[00:33:12] The Open Star Cluster NGC 6618 lies embedded in the nebulosity and causes gases from the

[00:33:19] nebula to shine due to intense radiation from all the hot young stars. Open star clusters are

[00:33:26] loosely bound groups of a few thousand stars which were originally all formed in the same

[00:33:30] molecular gas and dust cloud, but they're not as densely bound gravitationally as globular clusters.

[00:33:37] Open clusters generally survive for a few hundred million years, with the most massive

[00:33:41] ones surviving for maybe a few billion. In contrast, the more massive globular clusters

[00:33:46] exert so much stronger gravitational attraction on their members that they can survive for much

[00:33:51] longer, billions and billions of years. The nebula is thought to contain around 800 stars,

[00:33:57] including over 100 of the largest, most massive spectrotype O and B blue stars. More than a

[00:34:03] thousand additional stars are also being formed in the surrounding molecular gas and dust clouds.

[00:34:09] And with an age of just a million years, it's also one of the youngest clusters known in the galaxy.

[00:34:15] The cloud of interstellar material which formed the nebula is roughly 40 light years across

[00:34:20] and contains some 30,000 solar masses. Another spectacular sight worth searching for in

[00:34:26] Sagittarius is the Trifid Nebula, Messier 20. It's another large star forming emission nebula

[00:34:32] containing many very young hot stars. Located between 2,000 and 9,000 light years away,

[00:34:38] the Trifid Nebula has a diameter of approximately 50 light years. The outside of the Trifid is a

[00:34:44] bluish reflection nebula while the inner region is glowing pink thanks to ionized hydrogen.

[00:34:50] There are two dark bands dividing the Trifid Nebula into three regions or lobes.

[00:34:55] Hydrogen in the nebula is ionized by a central triple star which formed in the intersection

[00:35:00] between the two dark bands, creating its characteristic pink color. Another star

[00:35:05] forming region, NGC 6559, located some 5,000 light years away, contains both red emission

[00:35:12] and blue reflection regions. The grouping of the Lagoon Nebula, the Trifid Nebula and NGC 6559

[00:35:19] are known as the Sagittarius Triple and are a spectacular sight to go searching for in the

[00:35:25] night skies. But it doesn't end there. Another stunning object easily worth a look is the Red

[00:35:31] Spider Nebula, NGC 6537. It's a planetary nebula about 8,000 light years from Earth.

[00:35:38] It has a prominent two-lobe shape, possibly due to a binary companion or magnetic fields,

[00:35:43] and has an S-shaped symmetry with the lobes opposite each other appearing similar.

[00:35:48] This is believed due to the central companion to the central white dwarf.

[00:35:52] The central white dwarf, the remnant of the original star, produces a powerful and 10,000

[00:35:58] degree hot 3,000 km per second stellar wind which is generating 100 billion km high waves

[00:36:03] of supersonic shocks, formed as the local gas is being compressed and heated in front of the

[00:36:08] rapidly expanding lobes. Atoms caught in the shock waves are radiating invisible light,

[00:36:14] giving the nebula its unique spider-like shape and also contributing to the expansion of the nebula.

[00:36:19] The star at the center of the Red Spider Nebula is surrounded by a dust shell,

[00:36:23] making its exact properties hard to determine. We think its surface temperature is probably

[00:36:28] somewhere around 250,000 degrees, although a temperature of up to 500,000 degrees can't be

[00:36:33] ruled out, and that would make it among the hottest white dwarf stars known.

[00:36:38] Looking directly south is the star Polaris Australis, or more accurately Sigma Octantis,

[00:36:44] the nearest star we have in the southern hemisphere to the south celestial pole,

[00:36:48] and consequently the closest counterpart we have to the north star Polaris. However,

[00:36:53] Sigma Octantis is far harder to see than Polaris because it's much fainter.

[00:36:58] Located some 270 light years away, it's an orange giant reaching the end of its life.

[00:37:04] Turning to the southwest and just above the horizon this time of year, we find Canopus,

[00:37:08] the second brightest star in the night sky after Sirius. It's located 310 light years away and

[00:37:14] is the brightest star in the constellation Carina the Keel. Canopus is a supergiant,

[00:37:20] some 9 times the mass of the Sun and 71 times its diameter.

[00:37:25] The month of June also marks the first of two annual encounters with the Taurids meteor shower.

[00:37:31] The Taurids are generated as the Earth passes through the debris stream created by the comet

[00:37:36] 2P Encke, which itself is thought to be a piece of a larger comet that broke apart somewhere between

[00:37:41] 20,000 and 30,000 years ago, most likely following numerous interactions with the powerful gravitational

[00:37:47] field of the king of planets Jupiter. As their name suggests, the Taurids' radiant or apparent

[00:37:53] point of origin is in the direction of Taurus the Bull. The Taurids meteor shower is unique

[00:37:59] in that it's made up of larger more massive material, pebbles instead of dust grains.

[00:38:04] Earth passes through the stream twice every year, once now in June, then again in October

[00:38:09] called Halloween fireballs. The Taurids release material both by normal cometary activity and also

[00:38:14] occasionally by close encounters with the gravitational tidal force of the Earth and

[00:38:19] other planets, and this makes the Taurid stream of material the largest in the inner solar system.

[00:38:25] Now since this stream of material is rather spread out in space, Earth will take several weeks to

[00:38:29] pass through it, causing an extended period of meteor activity compared to the much smaller

[00:38:34] periods of activity associated with other meteor showers. Included in the stream is a denser flow

[00:38:40] of gravelly meteoroids called the Taurid swarm, thought to be a ribbon of rocks roughly 75 million

[00:38:46] by 150 million kilometers across. Occasionally, planet Earth passes through the larger meteoroids

[00:38:52] in the denser Taurid swarm. In fact, one of the larger chunks of the Taurid swarm is now thought

[00:38:58] to have caused the infamous Tunguska event in the skies over Siberia back on June 30, 1908.

[00:39:05] Astronomers believe the Tunguska event was the airburst of a 100-meter-wide meteor over the

[00:39:10] Tunguska River region of Russia causing mass devastation and flattening over 2,000 square

[00:39:16] kilometers of forest in the Matzdix. The blast was so bright it was enough to light up the night sky

[00:39:22] in London a third of the way around the planet. Tunguska remains the largest known Earth impact

[00:39:28] event in recorded history. It was considered a one-in-a-thousand-year event, assuming a random

[00:39:33] distribution of events over time. But new studies suggesting the event may have been caused by a

[00:39:39] Taurid swarm meteor, and with the Earth passing through that swarm periodically, this tends to

[00:39:44] change those odds quite significantly. If the study is correct, this swarm heightens the possibility

[00:39:50] of a cluster of large impacts on the Earth over a very short period of time.

[00:39:54] For the complicating matters, the June Taurids are actually two separate showers.

[00:39:59] The southern Taurids, associated with the comet 2P Encke, while the northern Taurids originate

[00:40:04] from the asteroid 2004 TG10, an eccentric kilometer-wide asteroid classified as a near-Earth

[00:40:10] object and potentially hazardous asteroid of the Apollo group. And that's the show for now.

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