Science
Telling time on the moon – Phys.org
A new era of lunar exploration is on the rise, with dozens of moon missions planned for the coming decade. Europe is in the forefront here, contributing to building the Gateway lunar station and the Orion spacecraft—set to return humans to our natural satellite—as well as developing its large logistic lunar lander, known as Argonaut. As dozens of missions will be operating on and around the moon and needing to communicate together and fix their positions independently from Earth, this new era will require its own time.
Accordingly, space organizations have started considering how to keep time on the moon. Having begun with a meeting at ESA’s ESTEC technology center in the Netherlands last November, the discussion is part of a larger effort to agree a common ‘LunaNet’ architecture covering lunar communication and navigation services.
Architecture for joint lunar exploration
“LunaNet is a framework of mutually agreed-upon standards, protocols and interface requirements allowing future lunar missions to work together, conceptually similar to what we did on Earth for joint use of GPS and Galileo,” explains Javier Ventura-Traveset, ESA’s Moonlight Navigation Manager, coordinating ESA contributions to LunaNet. “Now, in the lunar context, we have the opportunity to agree on our interoperability approach from the very beginning, before the systems are actually implemented.”
Timing is a crucial element, adds ESA navigation system engineer Pietro Giordano: “During this meeting at ESTEC, we agreed on the importance and urgency of defining a common lunar reference time, which is internationally accepted and towards which all lunar systems and users may refer to. A joint international effort is now being launched towards achieving this.”
Up until now, each new mission to the moon is operated on its own timescale exported from Earth, with deep space antennas used to keep onboard chronometers synchronized with terrestrial time at the same time as they facilitate two-way communications. This way of working will not be sustainable however in the coming lunar environment.
Once complete, the Gateway station will be open to astronaut stays, resupplied through regular NASA Artemis launches, culminating in a human return to the lunar surface, progressing to a crewed base near the lunar south pole. Meanwhile numerous uncrewed missions will also be in place—each Artemis mission alone will release numerous lunar CubeSats—and ESA will be putting down its Argonaut European Large Logistics Lander.
These missions will not only be on or around the moon at the same time, but they will often be interacting as well—potentially relaying communications for one another, performing joint observations or carrying out rendezvous operations.
Moonlight satellites on the way
“Looking ahead to lunar exploration of the future, ESA is developing through its Moonlight program a lunar communications and navigation service,” explains Wael-El Daly, system engineer for Moonlight. “This will allow missions to maintain links to and from Earth, and guide them on their way around the moon and on the surface, allowing them to focus on their core tasks. But also, Moonlight will need a shared common timescale in order to get missions linked up and to facilitate position fixes.”
And Moonlight will be joined in lunar orbit by an equivalent service sponsored by NASA—the Lunar Communications Relay and Navigation System. To maximize interoperability these two systems should employ the same timescale, along with the many other crewed and uncrewed missions they will support.
Fixing time to fix position
Jörg Hahn, ESA’s chief Galileo engineer and also advising on lunar time aspects comments: “Interoperability of time and geodetic reference frames has been successfully achieved here on Earth for Global Navigation Satellite Systems; all of today’s smartphones are able to make use of existing GNSS to compute a user position down to meter or even decimetre level.
“The experience of this success can be re-used for the technical long-term lunar systems to come, even though stable timekeeping on the moon will throw up its own unique challenges—such as taking into account the fact that time passes at a different rate there due to the Moon’s specific gravity and velocity effects.”
Setting global time
Accurate navigation demands rigorous timekeeping. This is because a satnav receiver determines its location by converting the times that multiple satellite signals take to reach it into measures of distance—multiplying time by the speed of light.
All the terrestrial satellite navigation systems, such as Europe’s Galileo or the United States’ GPS, run on their own distinct timing systems, but these possess fixed offsets relative to each other down to a few billionths of a second, and also to the UTC Universal Coordinated Time global standard.
The replacement for Greenwich Mean Time, UTC is part of all our daily lives: it is the timing used for Internet, banking and aviation standards as well as precise scientific experiments, maintained by the Paris-based Bureau International de Poids et Mesures (BIPM).
The BIPM computes UTC based on inputs from collections of atomic clocks maintained by institutions around the world, including ESA’s ESTEC technical center in Noordwijk, the Netherlands and the ESOC mission control center in Darmstadt, Germany.
Designing lunar chronology
Among the current topics under debate is whether a single organization should similarly be responsible for setting and maintaining lunar time. And also, whether lunar time should be set on an independent basis on the moon or kept synchronized with Earth.
The international team working on the subject will face considerable technical issues. For example, clocks on the moon run faster than their terrestrial equivalents—gaining around 56 microseconds or millionths of a second per day. Their exact rate depends on their position on the moon, ticking differently on the lunar surface than from orbit.
“Of course, the agreed time system will also have to be practical for astronauts,” explains Bernhard Hufenbach, a member of the Moonlight Management Team from ESA’s Directorate of Human and Robotic Exploration. “This will be quite a challenge on a planetary surface where in the equatorial region each day is 29.5 days long, including freezing fortnight-long lunar nights, with the whole of Earth just a small blue circle in the dark sky. But having established a working time system for the moon, we can go on to do the same for other planetary destinations.”
Finally, to work together properly, the international community will also have to settle on a common ‘selenocentric reference frame’, similar to the role played on Earth by the International Terrestrial Reference Frame, allowing the consistent measurement of precise distances between points across our planet. Suitably customized reference frames are essential ingredients of today’s GNSS systems.
“Throughout human history, exploration has actually been a key driver of improved timekeeping and geodetic reference models,” adds Javier. “It is certainly an exciting time to do that now for the moon, working towards defining an internationally agreed timescale and a common selenocentric reference, which will not only ensure interoperability between the different lunar navigation systems, but which will also foster a large number of research opportunities and applications in cislunar space.”
Provided by
European Space Agency
Citation:
Telling time on the moon (2023, February 27)
retrieved 27 February 2023
from https://phys.org/news/2023-02-moon.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.
A team of astronomers has discovered one of the biggest black holes ever found, taking advantage of a phenomenon called gravitational lensing.
The team, led by Durham University, UK, used gravitational lensing—where a foreground galaxy bends the light from a more distant object and magnifies it—and supercomputer simulations on the DiRAC HPC facility, which enabled the team to closely examine how light is bent by a black hole inside a galaxy hundreds of millions of light years from Earth.
They found an ultramassive black hole, an object over 30 billion times the mass of our sun, in the foreground galaxy—a scale rarely seen by astronomers.
This is the first black hole found using the technique, whereby the team simulates light traveling through the universe hundreds of thousands of times. Each simulation includes a different mass black hole, changing light’s journey to Earth.
When the researchers included an ultramassive black hole in one of their simulations the path taken by the light from the faraway galaxy to reach Earth matched the path seen in real images captured by the Hubble Space Telescope.
The findings are published today in the journal Monthly Notices of the Royal Astronomical Society.
[embedded content]
Lead author Dr. James Nightingale, Department of Physics, Durham University, said, “This particular black hole, which is roughly 30 billion times the mass of our sun, is one of the biggest ever detected and on the upper limit of how large we believe black holes can theoretically become, so it is an extremely exciting discovery.”
A gravitational lens occurs when the gravitational field of a foreground galaxy appears to bend the light of a background galaxy, meaning that we observe it more than once.
Like a real lens, this also magnifies the background galaxy, allowing scientists to study it in enhanced detail.
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Video still—black hole—lensing geometry. Credit: Durham University
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Video still—black hole—observed image. Credit: Durham University
Dr. Nightingale said, “Most of the biggest black holes that we know about are in an active state, where matter pulled in close to the black hole heats up and releases energy in the form of light, X-rays, and other radiation.”
“However, gravitational lensing makes it possible to study inactive black holes, something not currently possible in distant galaxies. This approach could let us detect many more black holes beyond our local universe and reveal how these exotic objects evolved further back in cosmic time.”
The study, which also includes Germany’s Max Planck Institute, opens up the tantalizing possibility that astronomers can discover far more inactive and ultramassive black holes than previously thought, and investigate how they grew so large.
The story of this particular discovery started back in 2004 when fellow Durham University astronomer, Professor Alastair Edge, noticed a giant arc of a gravitational lens when reviewing images of a galaxy survey.
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Video still—black hole—mass correct. Credit: Durham University
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Video still—black hole—mass too high. Credit: Durham University
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Video still—black hole—mass too low. Credit: Durham University
Fast forward 19 years and with the help of some extremely high-resolution images from NASA’s Hubble telescope and the DiRAC COSMA8 supercomputer facilities at Durham University, Dr. Nightingale and his team were able to revisit this and explore it further.
The team hopes that this is the first step in enabling a deeper exploration of the mysteries of black holes, and that future large-scale telescopes will help astronomers study even more distant black holes to learn more about their size and scale.
More information:
James Nightingale et al, Abell 1201: Detection of an Ultramassive Black Hole in a Strong Gravitational Lens, Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad587
Provided by
Durham University
Citation:
Light-bending gravity reveals one of the biggest black holes ever found (2023, March 28)
retrieved 28 March 2023
from https://phys.org/news/2023-03-light-bending-gravity-reveals-biggest-black.html
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part may be reproduced without the written permission. The content is provided for information purposes only.
Tonight, just after sunset, skywatchers across B.C. will be in for an eye-popping show.
Five planets — Mars, Uranus, Venus, Mercury and Jupiter — will be lined up in an arc and visible on the western horizon from almost anywhere on Earth.
“I like to call it, essentially, a cosmic coincidence,” said Andrew Ferreira, a public relations representative with the Vancouver branch of the Royal Astronomical Society of Canada.
“It’s purely just a coincidence that, you know, five planets happened to line up more or less from our perspective.”
In an interview with CBC, Ferreira said the best time to view the phenomenon will be just after the sun drops below the horizon. Keeping watch just after sunset is best, because as the night sky moves, “it’s essentially going to keep panning these planets down below the horizon.”
Ferreira’s suggestion is to spot the half-moon in the sky and trace a visual line down from there to see Mars. Below that will be Uranus and Venus. Below Venus will be Mercury, and closest to the horizon will be Jupiter.
Ferreira said Venus will outshine Uranus, but Uranus will be visible as a “greenish-blueish glow.” Mercury, he said, will be very faint but visible through binoculars, and people in downtown Vancouver or other urban centres might not be able to see Jupiter because of its low position on the horizon.
Getting away from city lights and buildings increases the chances for clearer viewing. Ferreira said giving your eyes a few minutes to adjust to the sky is also a good idea.
Great conditions for viewing
Of course, people hoping to catch the planetary procession will also benefit from clear skies overhead. And there’s good news on that front.
“The forecast for almost the entire province is looking great for a night-sky viewing,” said CBC meteorologist Johanna Wagstaffe.
“We have a high pressure system in place for B.C. which is bringing cloudless skies for almost everyone. The exceptions are a few high clouds that may sneak in tonight to northern B.C.”
“It may get a little chilly though with no clouds to keep the daytime heat in, so bundle up when you look up tonight.”
Alignments happen once or twice each year
As for the rarity of planetary alignments, Ferreira said ones like tonight happen once or twice each year. But an alignment of all the planets in the solar system, minus Earth, “that’s something like once every 200 or 300 years,” he said. “So it kind of depends on the objects and how many of them are lined up.”
Rare or not, Ferreira said events like tonight are always a joy, even for avid skywatchers like himself.
“It’s exciting being able to tell people about it — to get other people excited about what we do,” he said.
“I always tell people that astronomy is the easiest science to do because all you need is your eyes and the ground. You lie on your back and you look up and you know you’re doing astronomy.”
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An international team of researchers has used the NASA/ESA/CSA James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 230°C), and suggests that it has no significant atmosphere. This is the first detection of any form of light emitted by an exoplanet as small and as cool as the rocky planets in our own solar system. The result marks an important step in determining whether planets orbiting small active stars like TRAPPIST-1 can sustain atmospheres needed to support life. It also bodes well for Webb’s ability to characterise temperate, Earth-sized exoplanets using MIRI.
“These observations really take advantage of Webb’s mid-infrared capability,” said Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author on the study published today in the journal Nature. “No previous telescopes have had the sensitivity to measure such dim mid-infrared light.”
Rocky planets orbiting ultra cool red dwarfs
In early 2017, astronomers reported the discovery of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth. What is remarkable about the planets is their similarity in size and mass to the inner, rocky planets of our own solar system. Although they all orbit much closer to their star than any of our planets orbit the Sun – all could fit comfortably within the orbit of Mercury – they receive comparable amounts of energy from their tiny star.
TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and receives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system’s habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems.
“There are ten times as many of these stars in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” explained Greene. “But they are also very active – they are very bright when they’re young and they give off flares and X-rays that can wipe out an atmosphere.”
Co-author Elsa Ducrot from CEA in France, who was on the team that conducted the initial studies of the TRAPPIST-1 system, added, “It’s easier to characterise terrestrial planets around smaller, cooler stars. If we want to understand habitability around M stars, the TRAPPIST-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets.”
Detecting an atmosphere (or not)
Previous observations of TRAPPIST-1 b with the NASA/ESA Hubble Space Telescope, as well as NASA’s Spitzer Space Telescope, found no evidence for a puffy atmosphere, but were not able to rule out a dense one.
One way to reduce the uncertainty is to measure the planet’s temperature. “This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Pierre-Olivier Lagage from CEA, a co-author on the paper. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”
Astronomers can subtract the brightness of the star from the combined brightness of the star and planet to calculate how much infrared light is coming from the planet’s dayside. This is then used to calculate the dayside temperature.
The graph shows combined data from five separate observations made using MIRI’s F1500W filter, which only allows light with wavelengths ranging from 13.5-16.6 microns to pass through to the detectors. The blue squares are individual brightness measurements. The red circles show measurements that are “binned,” or averaged to make it easier to see the change over time. The decrease in brightness during the secondary eclipse is less than 0.1%. MIRI was able to detect changes as small as 0.027% (or 1 part in 3700).
This is the first thermal emission observation of TRAPPIST-1 b, or any planet as small as Earth and as cool as the rocky planets in the Solar System.
The observations are being repeated using a 12.8-micron filter in order to confirm the results and narrow down the interpretations.
MIRI was developed as a partnership between Europe and the USA: the main partners are ESA, a consortium of nationally funded European institutes, the Jet Propulsion Laboratory (JPL) and the University of Arizona. The instrument was nationally funded by the European Consortium under the auspices of the European Space Agency.
[Image description: At the top of the infographic is a diagram showing a planet moving behind its star (a secondary eclipse). Below the diagram is a graph showing the change in brightness of 15-micron light emitted by the star-planet system over the course of 3.5 hours. The infographic shows that the brightness of the system decreases markedly as the planet moves behind the star.]
Credit:
NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)
The team used a technique called secondary eclipse photometry, in which MIRI measured the change in brightness from the system as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to give off its own visible light, it does have an infrared glow. By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.
Measuring minuscule changes in brightness
Webb’s detection of a secondary eclipse is itself a major milestone. With the star more than 1,000 times brighter than the planet, the change in brightness is less than 0.1%.
“There was also some fear that we’d miss the eclipse. The planets all tug on each other, so the orbits are not perfect,” said Taylor Bell, the post-doctoral researcher at the Bay Area Environmental Research Institute who analysed the data. “But it was just amazing: The time of the eclipse that we saw in the data matched the predicted time within a couple of minutes.”
Analysis of data from five separate secondary eclipse observations indicates that TRAPPIST-1 b has a dayside temperature of about 500 kelvins, or roughly 230°C. The team thinks the most likely interpretation is that the planet does not have an atmosphere.
If the heat energy from the star were distributed evenly around the planet (for example, by a circulating carbon dioxide-free atmosphere), the temperature at 15 microns would be 400 K (125°C). If the atmosphere had a substantial amount of carbon dioxide, it would emit even less 15-micron light and would appear to be even cooler.
Although TRAPPIST-1 b is hot by Earth standards, it is cooler than the dayside of Mercury, which consists of bare rock and no significant atmosphere. Mercury receives about 1.6 times more energy from the Sun than TRAPPIST-1 b does from its star.
MIRI was developed as a partnership between Europe and the USA: the main partners are ESA, a consortium of nationally funded European institutes, the Jet Propulsion Laboratory (JPL) and the University of Arizona. The instrument was nationally funded by the European Consortium under the auspices of the European Space Agency.
[Image description: Infographic titled, “Rocky Exoplanet TRAPPIST-1 b Dayside Temperature Comparison, MIRI F1500W” showing five planets plotted along a horizontal temperature scale: Earth, TRAPPIST-1 b, Mercury, and two different models of TRAPPIST-1 b.]
Credit:
NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)
“We compared the results to computer models showing what the temperature should be in different scenarios,” explained Ducrot. “The results are almost perfectly consistent with a blackbody made of bare rock and no atmosphere to circulate the heat. We also didn’t see any signs of light being absorbed by carbon dioxide, which would be apparent in these measurements.”
This research was conducted as part of Guaranteed Time Observation (GTO) program 1177, which is one of eight approved GTO and General Observer (GO) programs designed to help fully characterise the TRAPPIST-1 system. Additional secondary eclipse observations of TRAPPIST-1 b are currently in progress, and now that they know how good the data can be, the team hopes to eventually capture a full phase curve showing the change in brightness over the entire orbit. This will allow them to see how the temperature changes from the day to the nightside and confirm if the planet has an atmosphere or not.
“There was one target that I dreamed of having,” said Lagage, who worked on the development of the MIRI instrument for more than two decades. “And it was this one. This is the first time we can detect the emission from a rocky, temperate planet. It’s a really important step in the story of discovering exoplanets.”
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