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Mobile phones are so ubiquitous that we typically don’t think about how they work. They just do, much to our benefit, and sometimes annoyance. But the key to their function is a vast array of radio transmission towers. These cell towers span a large percentage of Earth’s land surface, particularly in heavily populated areas, and they transmit microwave signals all the time. With all those cell towers emitting all those radio signals, a fun question to ask is whether those signals could be detected by an alien civilization.

The answer to this question was recently published in the Monthly Notices of the Royal Astronomical Society, and it’s worth the read. The paper starts by noting how the radio signals streaming into space have changed. In the 20th century, the bulk of radio transmissions were those from commercial radio and television stations. Now those transmissions are dwarfed by those of mobile communications. Military radar transmissions are still the most powerful source of Earth’s radio leakage, but cell towers now fill the second position.

Each cell tower emits a radio signal with a power of 100 – 200 Watts. Given the number of towers and the amount of radio leakage, that amounts to a few gigawatts beamed into space. If we assume an alien civilization has sophisticated radio astronomy, similar to our Event Horizon Telescope, then our transmissions should be detectable within a dozen light-years or so.

But that depends on where the aliens are in our sky. Cell towers emit most of their radio power parallel to the surface of the Earth, so a tower signal is strongest when it is rising or setting as seen from the alien star. And since the majority of towers are in the northern hemisphere, an alien star in the northern hemisphere will get a stronger signal than one in the southern hemisphere.

One other complication is all the tower signals are different, and they overlap in such a way that an alien civilization wouldn’t be able to distinguish any specific messages. You don’t need to worry about aliens listening in on your personal phone calls. But they could still use the signals to find out some interesting things about Earth. Since the distribution of towers roughly corresponds to our population distribution, the aliens could get a measure of Earth’s rotation and axial tilt. They would also have a measure of Earth’s land distribution, and over time could study how our population distributions change.

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Calculated Earth signal as seen from HD 95735, about 8 light-years from Earth. Credit: Saide, et al

As an example, the team modeled signals as seen from three nearby stars. Alpha Centauri is in the southern hemisphere, but just 4 light-years away, so it should get a measurable signal from us. Barnard’s Star (6 light-years away) and HD 95735 (8 light-years away) are in the northern hemisphere, and would likewise get good radio data from Earth. All three of these star systems are known to have planets, though none are known to have a potentially habitable world.

As humanity transitions to more modern mobile technology such as 5G, tower signals will become even stronger, which means even more nearby stars would have a detectable signal from Earth. It may be just a matter of time before our phone signals reach out and touch alien minds.

Reference: Saide, Ramiro C., M. A. Garrett, and N. Heeralall-Issur. “Simulation of the Earth’s radio-leakage from mobile towers as seen from selected nearby stellar systems.” Monthly Notices of the Royal Astronomical Society (2023): stad378.

The post Aliens Could Map Earth From its Mobile Phone Towers appeared first on Universe Today.

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Astronomers are Searching for a Galaxy-Wide Transmitter Beacon at the Center of the Milky Way

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June 4, 2023

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It has been over sixty years since the first Search for Extraterrestrial Intelligence (SETI) survey occurred. This was Project Ozma, a survey led by Dr. Frank Drake (who devised the Drake Equation) that used the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, to listen for radio transmissions from Epsilon Eridani and Tau Ceti. While the search revealed nothing of interest, it paved the way for decades of research, theory, and attempts to find evidence of technological activity (aka. “technosignatures”).

The search continues today, with researchers using next-generation instruments and analytical methods to find the “needle in the cosmic haystack.” This is the purpose behind Breakthrough Listen Investigation for Periodic Spectral Signals (BLIPSS), a collaborative SETI project led by Cornell graduate student Akshay Suresh to look for technosignatures at the center of the Milky Way. In a recent paper, Suresh and his team shared their initial findings, which were made possible thanks to data obtained by the Greenbank Observatory and a proprietary algorithm they developed.

Suresh is a Ph.D. candidate at the Cornell Center for Astrophysics and Planetary Science who leads the BLIPPS campaign, a collaboration between Cornell University, the SETI Institute, and Breakthrough Listen. He and his colleagues were joined by astrophysicists from the Cahill Center for Astronomy and Astrophysics, the Institute for Mathematics, Astrophysics, and Particle Physics (IMAPP), the Institute of Space Sciences and Astronomy, and the International Centre for Radio Astronomy Research (ICRAR). Their paper, “A 4–8 GHz Galactic Center Search for Periodic Technosignatures,” appeared on May 30th in The Astronomical Journal.

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The Karl Jansky Very Large Array at night, with the Milky Way visible in the sky. Credit: NRAO/AUI/NSF; J. Hellerman

To date, all SETI surveys have been dedicated to looking for evidence of artificial radio transmissions. The accepted theory is that radio signatures would fall into one of two categories: narrowband intentional beacon emissions and broadband radiation leakage from radio transmitters. Of the two, the spectrotemporal characteristics (frequency over time) of radiation leakage are much harder to speculate about and likely to be weaker. For this reason, most modern SETI efforts have focused on looking for wideband searches for narrowband beacons from planetary systems or neighboring galaxies.

In particular, a rotating beacon near Galactic Center (GC) is considered a promising technosignature to SETI researchers. For an advanced species, such a beacon would provide a means for communicating with the entire galaxy without the need for direct contact. For species dying to know if they are alone in the Universe but not so eager as to advertise their location, a beacon is doubly attractive because it would also allow some anonymity to be maintained. As Suresh told Universe Today via email:

“From a game theory perspective, the core of the Milky Way is a likely “Schelling point” by which different alien worlds may establish communication without prior contact. For instance, intelligent aliens may choose to transmit beacons toward the center of the Milky Way to reach a maximum number of targets. Equivalently, such aliens may also transmit directly away from the center of the Milky Way, knowing that societies like ours will look towards the core of the galaxy.”

For their search, the team employed a fast folding algorithm (FFA), an open-source machine learning software designed to detect periodic events within time series data. They first tested this algorithm on known pulsars, successfully detecting the expected periodic emissions. They then consulted datasets obtained by the 100-meter Green Bank Telescope (GBT) – part of the Breakthrough Listen’s network – on a region at the center of the Milky Way during a 4.5-hour observing period. This region measures 50 light-years in diameter and encompasses over half a million stars.

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Jupiter’s “Stripes” Change Color. Now We Might Know Why

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June 4, 2023

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While Jupiter’s Great Red Spot is one of the most well-known spectacles in the solar system, Jupiter’s clouds and stripes that are responsible for the planet’s weather patterns are highly regarded, as well. Though not nearly as visible in an amateur astronomy telescope, Jupiter’s multicolored, rotating, and swirling cloud stripes are a sight to behold for any astronomy fan when seen in up-close images. And, what makes these stripes unique is they have been observed to change color from time to time, but the question of what causes this color change to occur has remained elusive.

This is what a recent study published in Nature Astronomy hopes to address as an international team of researchers examine how Jupiter’s massive magnetic field could be responsible for Jupiter’s changing stripe colors. This study was led by Dr. Kumiko Hori of Kobe University and Dr. Chris Jones of the University of Leeds and holds the potential to help scientists better understand how a planet’s magnetic field could influence a planet’s weather patterns. In this case, Jupiter’s massive magnetic field influencing its massive, swirling clouds.

“If you look at Jupiter through a telescope, you see the stripes, which go round the equator along lines of latitude,” explains Dr. Jones. “There are dark and light belts that occur, and if you look a little bit more closely, you can see clouds zipping around carried by extraordinarily strong easterly and westerly winds. Near the equator, the wind blows eastward but as you change latitude a bit, either north or south, it goes westward. And then if you move a little bit further away it goes eastward again. This alternating pattern of eastward and westward winds is quite different from weather on Earth.”

While previous studies have demonstrated that Jupiter’s appearance is somehow altered by infrared fluctuations approximately 50 km (31 mi) below the gas cloud surface, this most recent study demonstrates the infrared fluctuations could be caused by Jupiter’s magnetic field, the source of which, like Earth, is far deeper inside the planet.

“Every four or five years, things change,” said Dr. Jones. “The colors of the belts can change and sometimes you see global upheavals when the whole weather pattern goes slightly crazy for a bit, and it has been a mystery as to why that happens.”

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Infrared images of Jupiter obtained by a ground-based telescope displaying changes in the color of Jupiter’s clouds between 2001 and 2011 (dashed blue lines). (Credit: Arrate Antuñano/NASA/IRTF/NSFCam/SpeX)

For the study, the researchers analyzed data collected over several years from NASA’s Juno spacecraft to both observe and measure variations in Jupiter’s magnetic field, more commonly known as oscillations. Despite Jupiter’s massive radiation belt which can cause immense harm to any spacecraft, Juno has been orbiting the solar system’s largest planet since 2016 and is frequently lauded for it still being active despite the constant bombardment from the radiation.

From the data, the team was able to monitor the magnetic field’s waves and oscillations. They focused on a specific area of the magnetic field dubbed the Great Blue Spot, which is invisible to the naked eye and located near Jupiter’s equator. While this spot has been observed to be traveling eastwards on Jupiter, the data from this study indicates the spot is slowing down, which the team interprets as the start of an oscillation within the magnetic field, meaning the spot could eventually slow enough to where it reverses direction and starts traveling westwards.

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Still image taken from a video animation featuring Jupiter’s massive magnetic field at one instant in time, specifically its Great Blue Spot located near
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CRS-28 Mission

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June 3, 2023

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SpaceX is targeting Saturday, June 3 for Falcon 9’s launch of Dragon’s 28th Commercial Resupply Services (CRS-28) mission to the International Space Station from Launch Complex 39A (LC-39A) at NASA’s Kennedy Space Center in Florida. The instantaneous launch window is at 12:35 p.m. ET (16:35 UTC) and a backup launch opportunity is available on Sunday, June 4 at 12:12 p.m. ET (16:12 UTC).

This is the fifth flight of the first stage booster supporting this mission, which previously launched Crew-5, GPS III Space Vehicle 06, Inmarsat I-6 F2, and one Starlink mission. Following stage separation, Falcon 9 will land on the A Shortfall of Gravitas droneship in the Atlantic Ocean.

CRS-28 is the fourth flight for this Dragon spacecraft, which previously flew CRS-21, CRS-23, and CRS-25 to the space station. After an approximate 41-hour flight, Dragon will autonomously dock with the orbiting laboratory on Monday, June 5 at approximately 5:38 a.m. ET (9:38 UTC).

A live webcast of this mission will begin about 20 minutes prior to liftoff.

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