Earthshine is one of the most spectacular sights in our night sky. Yet, this astronomical phenomenon is slowly vanishing, and this is providing us with a new warning sign for the climate.
Gaze up at a thin Crescent Moon as it hangs above the horizon, and you will often be able to dimly make out the features that are immersed in the shadow of the Moon’s dark side. This phenomenon is known as Earthshine.
Sunlight reflected from Earth shines upon the Moon’s dark side, in a phenomenon called Earthshine. Credit: Science@NASA
Earthshine results from Earth’s albedo. Of all the incoming sunlight that reaches Earth, roughly one-third gets directly reflected back into space by bright cloud tops and icy surfaces.
Some of this reflected sunlight shines onto the Moon’s surface. This effect is best seen just before and just after a New Moon. That’s when the greatest amount of dark lunar surface is lit by the greatest amount of reflected light from Earth. Anyone looking up at the Moon on those nights will be able to pick out the most prominent features of the lunar surface, even though they are not lit by the direct light of the Sun.
Viewing the Moon from Earth and Earth from the Moon during any month reveals how their phases are complementary. As shown in this image, anyone standing on the lunar surface during a thin Crescent Moon would see a brightly lit “nearly full” Earth. Credit: NASA
However, according to a new study, this phenomenon is slowly disappearing.
Researchers gathered two decades worth of observations of Earthshine, from 1998 to 2017, taken at the Big Bear Solar Observatory, in San Bernardino National Forest, east of Los Angeles, California. The data they collected revealed that Earthshine had dimmed over that time, by about 0.5 per cent. Since the dimming they observed did not match up with changes in the Sun’s brightness during that same time period, that means the dimming is being caused by Earth.
In other words, Earth’s albedo is decreasing, thus the planet is now reflecting less sunlight back into space than it was 20 years ago.
“The albedo drop was such a surprise to us when we analyzed the last three years of data after 17 years of nearly flat albedo,” Philip Goode, the lead researcher on the study from the New Jersey Institute of Technology, said in a press release from the American Geophysical Union (AGU).
This graph shows two decades worth of Earthshine data (black points), alongside data from NASA’s Clouds and the Earth’s Radiant Energy System (CERES) instruments in orbit (blue points). Both reveal that Earth’s albedo is decreasing. CERES detected a significant drop in albedo in 2019. Credit: Goode et al. (2021), Geophysical Research Letters.
While the slow disappearance of Earthshine would be terrible for stargazers, there is a much more significant and troubling impact from this discovery.
Over the years, one of the uncertainties in Earth’s climate system has been whether rising ocean temperatures would increase or decrease cloud cover.
If it increased cloud cover, it could create a self-limiting effect on climate change. Greater cloud cover would increase the amount of sunlight being reflected back into space. As a result, with less sunlight reaching the surface, it would reduce the amount of heat being added to the climate system.
On the other hand, if warming oceans resulted in less cloud cover, it would lower the planet’s albedo. More sunlight would reach the ground, which would result in more heat being added to the climate system. Over time, this would increase the rate of global warming and make the impacts of climate change worse.
Photographed from the International Space Station on July 31, 2011, this image shows the Crescent Moon shining above the limb of Earth, along with the different layers of the atmosphere (troposphere in orange, stratosphere in blue, fading into the mesosphere). The dark side of the Moon is dimly illuminated by the phenomenon of Earthshine. Credit: NASA
This new study found that, along with the detected decrease in Earthshine from their observations, NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project also saw a reduction in the amount of cloud cover over the eastern Pacific Ocean. The CERES instruments, carried by NASA’s Terra and Aqua satellites, found fewer bright, low-lying clouds over a region of the Pacific Ocean off the west coasts of North and South America.
This reduction in clouds is over a region of the ocean where previous studies have shown sea surface temperatures to be on the rise. The increase in temperatures is likely due to changes in a large-scale climate pattern known as the Pacific Decadal Oscillation (PDO).
Thus, based on the findings of this study, it would appear that warmer oceans are reducing the amount of cloud cover, which is very bad news.
Also, although the drop in albedo is only 0.5 per cent, the amount of extra heat it adds to our climate system is nearly the same as what human activity added over the same time period.
“The two-decade decrease in earthshine-derived albedo corresponds to an increase in radiative forcing of about 0.5 Watts per square metre, which is climatologically significant,” the researchers wrote. “For comparison, total anthropogenic forcing increased by about 0.6 Watts per square metre over the same period.”
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
The European Space Agency is fast-tracking a new mission called Ramses, which will fly to near-Earth asteroid 99942 Apophis and join the space rock in 2029 when it comes very close to our planet — closer even than the region where geosynchronous satellites sit.
Ramses is short for Rapid Apophis Mission for Space Safety and, as its name suggests, is the next phase in humanity’s efforts to learn more about near-Earth asteroids (NEOs) and how we might deflect them should one ever be discovered on a collision course with planet Earth.
In order to launch in time to rendezvous with Apophis in February 2029, scientists at the European Space Agency have been given permission to start planning Ramses even before the multinational space agency officially adopts the mission. The sanctioning and appropriation of funding for the Ramses mission will hopefully take place at ESA’s Ministerial Council meeting (involving representatives from each of ESA’s member states) in November of 2025. To arrive at Apophis in February 2029, launch would have to take place in April 2028, the agency says.
This is a big deal because large asteroids don’t come this close to Earth very often. It is thus scientifically precious that, on April 13, 2029, Apophis will pass within 19,794 miles (31,860 kilometers) of Earth. For comparison, geosynchronous orbit is 22,236 miles (35,786 km) above Earth’s surface. Such close fly-bys by asteroids hundreds of meters across (Apophis is about 1,230 feet, or 375 meters, across) only occur on average once every 5,000 to 10,000 years. Miss this one, and we’ve got a long time to wait for the next.
When Apophis was discovered in 2004, it was for a short time the most dangerous asteroid known, being classified as having the potential to impact with Earth possibly in 2029, 2036, or 2068. Should an asteroid of its size strike Earth, it could gouge out a crater several kilometers across and devastate a country with shock waves, flash heating and earth tremors. If it crashed down in the ocean, it could send a towering tsunami to devastate coastlines in multiple countries.
Over time, as our knowledge of Apophis’ orbit became more refined, however, the risk of impact greatly went down. Radar observations of the asteroid in March of 2021 reduced the uncertainty in Apophis’ orbit from hundreds of kilometers to just a few kilometers, finally removing any lingering worries about an impact — at least for the next 100 years. (Beyond 100 years, asteroid orbits can become too unpredictable to plot with any accuracy, but there’s currently no suggestion that an impact will occur after 100 years.) So, Earth is expected to be perfectly safe in 2029 when Apophis comes through. Still, scientists want to see how Apophis responds by coming so close to Earth and entering our planet’s gravitational field.
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“There is still so much we have yet to learn about asteroids but, until now, we have had to travel deep into the solar system to study them and perform experiments ourselves to interact with their surface,” said Patrick Michel, who is the Director of Research at CNRS at Observatoire de la Côte d’Azur in Nice, France, in a statement. “Nature is bringing one to us and conducting the experiment itself. All we need to do is watch as Apophis is stretched and squeezed by strong tidal forces that may trigger landslides and other disturbances and reveal new material from beneath the surface.”
The Goldstone radar’s imagery of asteroid 99942 Apophis as it made its closest approach to Earth, in March 2021. (Image credit: NASA/JPL–Caltech/NSF/AUI/GBO)
By arriving at Apophis before the asteroid’s close encounter with Earth, and sticking with it throughout the flyby and beyond, Ramses will be in prime position to conduct before-and-after surveys to see how Apophis reacts to Earth. By looking for disturbances Earth’s gravitational tidal forces trigger on the asteroid’s surface, Ramses will be able to learn about Apophis’ internal structure, density, porosity and composition, all of which are characteristics that we would need to first understand before considering how best to deflect a similar asteroid were one ever found to be on a collision course with our world.
Besides assisting in protecting Earth, learning about Apophis will give scientists further insights into how similar asteroids formed in the early solar system, and, in the process, how planets (including Earth) formed out of the same material.
One way we already know Earth will affect Apophis is by changing its orbit. Currently, Apophis is categorized as an Aten-type asteroid, which is what we call the class of near-Earth objects that have a shorter orbit around the sun than Earth does. Apophis currently gets as far as 0.92 astronomical units (137.6 million km, or 85.5 million miles) from the sun. However, our planet will give Apophis a gravitational nudge that will enlarge its orbit to 1.1 astronomical units (164.6 million km, or 102 million miles), such that its orbital period becomes longer than Earth’s.
It will then be classed as an Apollo-type asteroid.
Ramses won’t be alone in tracking Apophis. NASA has repurposed their OSIRIS-REx mission, which returned a sample from another near-Earth asteroid, 101955 Bennu, in 2023. However, the spacecraft, renamed OSIRIS-APEX (Apophis Explorer), won’t arrive at the asteroid until April 23, 2029, ten days after the close encounter with Earth. OSIRIS-APEX will initially perform a flyby of Apophis at a distance of about 2,500 miles (4,000 km) from the object, then return in June that year to settle into orbit around Apophis for an 18-month mission.
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Furthermore, the European Space Agency still plans on launching its Hera spacecraft in October 2024 to follow-up on the DART mission to the double asteroid Didymos and Dimorphos. DART impacted the latter in a test of kinetic impactor capabilities for potentially changing a hazardous asteroid’s orbit around our planet. Hera will survey the binary asteroid system and observe the crater made by DART’s sacrifice to gain a better understanding of Dimorphos’ structure and composition post-impact, so that we can place the results in context.
The more near-Earth asteroids like Dimorphos and Apophis that we study, the greater that context becomes. Perhaps, one day, the understanding that we have gained from these missions will indeed save our planet.
