However, shortly after takeoff disaster strikes the mission, and the chances of the crew making it to Enceladus, let alone back home, look grim.
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Ice Moon – The Boxset
All four bestselling books of the Ice Moon series are now offered as a set, available only in e-book format.
The Enceladus Mission: Is there really life on Saturn's moon Enceladus? ILSE, the International Life Search Expedition, makes its way to the icy world where an underground ocean is suspected to be home to primitive life forms.
The Titan Probe: An old robotic NASA probe mysteriously awakens on the methane moon of Titan. The ILSE crew tries to solve the riddle—and discovers a dangerous secret.
The Io Encounter: Finally bound for Earth, ILSE makes it as far as Jupiter when the crew receives a startling message. The volcanic moon Io may harbor a looming threat that could wipe out Earth as we know it.
Return to Enceladus: The crew gets an offer to go back to Enceladus. Their mission—to recover the body of Dr. Marchenko, left for dead on the original expedition. Not everyone is working toward the same goal.
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Proxima Rising
Late in the 21st century, Earth receives what looks like an urgent plea for help from planet Proxima Centauri b in the closest star system to the Sun. Astrophysicists suspect a massive solar flare is about to destroy this heretofore-unknown civilization. Earth’s space programs are unequipped to help, but an unscrupulous Russian billionaire launches a secret and highly-specialized spaceship to Proxima b, over four light-years away. The unusual crew faces a Herculean task—should they survive the journey. No one knows what to expect from this alien planet.
3.99 $ – hard-sf.com/links/610690
The Hole
A mysterious object threatens to destroy our solar system. The survival of humankind is at risk, but nobody takes the warning of young astrophysicist Maribel Pedreira seriously. At the same time, an exiled crew of outcasts mines for rare minerals on a lone asteroid.
When other scientists finally acknowledge Pedreira’s alarming discovery, it becomes clear that these outcasts are the only ones who may be able to save our world, knowing that The Hole hurtles inexorably toward the sun.
3.99 $ – hard-sf.com/links/527017
Mars Nation 1
NASA finally made it. The very first human has just set foot on the surface of our neighbor planet. This is the start of a long research expedition that sent four scientists into space.
But the four astronauts of the NASA crew are not the only ones with this destination. The privately financed ‘Mars for Everyone’ initiative has also targeted the Red Planet. Twenty men and women have been selected to live there and establish the first extraterrestrial settlement.
Challenges arise even before they reach Mars orbit. The MfE spaceship Santa Maria is damaged along the way. Only the four NASA astronauts can intervene and try to save their lives.
No one anticipates the impending catastrophe that threatens their very existence—not to speak of the daily hurdles that an extended stay on an alien planet sets before them. On Mars, a struggle begins for limited resources, human cooperation, and just plain survival.
3.99 $ – hard-sf.com/links/762824
Impact: Titan
How to avoid killing Earth if you don't even know who sent the killer
250 years ago, humanity nearly destroyed itself in the Great War. Shortly before, a spaceship full of researchers and astronauts had found a new home on Saturn's moon, Titan, and survived by having their descendants genetically adapted to the hostile environment.
The Titanians, as they call themselves, are proud of their cooperative and peaceful society, while unbeknownst to them, humanity is slowly recovering back on Earth. When a 20-mile-wide chunk of rock escapes the asteroid belt and appears to be on a collision course with Earth, the Titanians fear it must look as if they launched the deadly bombardment. Can they prevent the impact and thus avoid an otherwise inevitable war with the Earthlings?
3.99 $ – hard-sf.com/links/1433312
A Guided Tour of Multi-Messenger Astronomy
For millennia, humans looked at the sky with their naked eyes.
Then came the telescope. Celestial bodies looked closer and clearer, but in principle, one still gained the same information. Next, scientists discovered that there is a continuous electromagnetic spectrum. Gamma and X-ray radiation, microwave radiation, ultraviolet and visible light, infrared, and radio emissions are all of the same nature, but have different frequencies, and thus transmit different information.
Electromagnetism is not the only source of data from space. Other fundamental forces also convey information about cosmic objects. Today, therefore, we speak of ‘multi-messenger astronomy.’ It is based on the coordinated observation and interpretation of different messenger signals. Interplanetary probes can visit objects within the solar system, but beyond that, scientists must rely on special ‘extrasolar’ messengers. These four extrasolar messengers include the aforementioned electromagnetic radiation, plus gravitational waves, neutrinos, and cosmic rays. They are generated by different astrophysical processes, and therefore reveal different information about their sources.
The most important multi-messenger research subjects outside the heliosphere are expected to include compact binary pairs (black holes and neutron stars), supernovae, irregular neutron stars, gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and relativistic jets. Just about any object reveals more about itself when observed in all available wavelengths and with all messengers.
In the following pages, I describe individual measurement methods and their special features.
Gamma Astronomy
Gamma rays represent the most energetic form of electromagnetic radiation. Their photons (light particles) reach energies of more than 100 keV. The cosmic processes that emit gamma rays are diverse, but mostly identical to those that emit X-rays, except that they occur at higher energies. Thus, where gamma rays are found, X-rays are often encountered as well. These include electron-positron annihilation, the inverse Compton effect, and in some cases, the decay of radioactive material (gamma decay) in space, which is possible in extreme events such as supernovae and hypernovae, and when matter comes under extreme conditions, such as in pulsars and blazars.
The highest photon energies measured so far are in the TeV range, the record being held by the Crab Nebula, which delivered photons of up to 80 TeV in 2004.
Long before experiments could detect gamma rays emitted by cosmic sources, scientists knew that the universe must produce them. These processes include interactions of cosmic rays with interstellar gas, supernova explosions, and interactions of energetic electrons with magnetic fields. However, it took until the 1960s before we were able to detect these emissions.
Indeed, most gamma rays coming from space are absorbed by the Earth’s atmosphere, so gamma-ray astronomy could not develop until it was possible to get detectors beyond most of the atmosphere using balloons and spacecraft. The first gamma-ray telescope, launched into orbit on the U.S. Explorer 11 satellite in 1961, caught fewer than 100 cosmic gamma-ray photons. They appeared to come from all directions in the universe, suggesting some sort of uniform gamma-ray background. Such a background would be expected from the interaction of cosmic rays with interstellar gas.
The first true astrophysical gamma-ray sources were solar flares that revealed a strong 2.223 MeV line. This line is developed during the formation of deuterium by the union of a neutron with a proton. Significant gamma-ray emissions from the Milky Way were first registered in 1967 by the detector aboard the OSO 3 satellite. It found 621 events attributable to cosmic gamma rays.
The field of gamma-ray astronomy made great leaps forward with the SAS-2 (1972) and Cos-B (1975-1982) satellites. These two satellites provided a glimpse into the high-energy universe. They confirmed earlier findings regarding the gamma-ray background, produced t
he first detailed map of the sky at gamma-ray wavelengths, and discovered a number of point sources. However, the instruments’ resolutions were not sufficient to identify most of these point sources as specific visible stars or star systems.
An important discovery in gamma-ray astronomy came from military satellites in the late 1960s and early 1970s. Detectors aboard the Vela series of satellites, designed to detect gamma-ray bursts from atomic bomb explosions, began recording gamma-ray bursts in space instead. Later detectors found that these GRBs last from fractions of a second to minutes, can appear suddenly and from unexpected directions, flicker, and then fade after briefly dominating the gamma-ray sky.
To this day, the sources of these mysterious high-energy flashes remain a mystery. In any case, they appear to come from far across the universe. The most plausible theory at present is that at least some of them come from so-called hypernova explosions—supernovas that produce black holes rather than neutron stars.
X-ray astronomy
X-ray astronomy, of course, deals with the observation of X-rays coming from astronomical objects. However, the Earth’s atmosphere absorbs X-rays, so instruments to detect them must be carried to high altitudes by balloons, sounding rockets, and satellites.
X-rays are emitted by astronomical objects containing extremely hot gases with temperatures ranging from about one million degrees Kelvin (K) to hundreds of millions of degrees Kelvin. Although science predicted that the sun and the stars had to be important X-ray sources, there was no way to verify this for a long time.
The existence of solar X-rays was only confirmed in the middle of the 20th century by V-2 rockets, which had been converted to sounding rockets. The discovery of extraterrestrial X-rays was the primary or secondary task of several satellites launched since 1958. The first cosmic X-ray source outside the solar system was discovered by a sounding rocket in 1962. The source was named Scorpius X-1 (Sco X-1). The X-ray emission from Scorpius X-1 is 10,000 times greater than in the visual range, while that from the sun is about a million times less. In addition, the object’s energy emission in the X-ray region is 100,000 times greater than the sun’s total emission in all wavelengths. It is now known that Sco X-1 is a neutron star that sucks matter from its companion.
In the meantime, astronomers have discovered many thousands of X-ray sources. Moreover, we now know that the space between galaxies in galaxy clusters is filled with a very hot but highly diluted gas with a temperature of between 100 and 1,000 megakelvin. The total amount of hot gas in visible galaxies is five to ten times their total mass.
Today, specialized telescopes aboard satellites are used to observe X-ray sources. These currently include the XMM-Newton observatory (low to medium energy X-rays 0.1-15 keV) and the INTEGRAL satellite (high energy X-rays 15-60 keV). The European Space Agency launched both of these, and NASA has the Swift and Chandra observatories in orbit.
The GOES 14 spacecraft carries a Solar X-ray Imager that monitors the sun’s X-rays for early detection of solar flares, coronal mass ejections, and other phenomena that affect the space environment. It was launched into orbit at 22:51 GMT on June 27, 2009, from Space Launch Complex 37B at Cape Canaveral Air Force Station.
On January 30, 2009, the Russian Federal Space Agency successfully launched the Koronas-Foton (CORONAS-Photon) which has several X-ray detection experiments on board, including the TESIS telescope/spectrometer FIAN with the SphinX soft X-ray spectrophotometer.
ISRO (India) launched the Astrosat multi-wavelength space observatory into orbit in 2015. One of the unique features of the Astrosat mission is that it enables simultaneous multi-wavelength observations of various astronomical objects with a single satellite. Astrosat observes the universe in the optical and ultraviolet regions, and the low- and high-energy X-ray regions, of the electromagnetic spectrum, while most other scientific satellites can only observe a narrow range of the wavelength band.
The Astro-rivelatore Gamma a Immagini LEggero (AGILE) gamma-ray observatory satellite of the Italian Space Agency (ASI), has the Super-AGILE detector for hard X-rays from 15-45 keV on board. It was launched on April 23, 2007, with the Indian PSLV-C8.
The Hard X-ray Modulation Telescope (HXMT) is a Chinese X-ray space observatory launched on June 15, 2017, to observe black holes, neutron stars, active galactic nuclei, and other phenomena by their X-ray and gamma-ray emissions.
China’s CNSA launched the ‘Lobster-Eye X-ray Satellite’ on July 25, 2020. It is the first in-orbit telescope to use an ultra-large field of view to search for dark matter signals in the X-ray energy range.
Where did X-ray radiation come from, and what types of objects can we observe in this part of the spectrum? Quite different types of astrophysical objects emit, fluoresce, or reflect X-rays, from galaxy clusters to black holes in active galactic nuclei (AGN) to galactic objects such as supernova remnants, stars, and binaries containing a white dwarf (cataclysmic variable stars and super-soft X-ray sources), a neutron star, or a black hole (X-ray binaries).
But some objects in the solar system also emit X-rays. The most notable is the moon, with most of its X-ray brightness coming from reflected solar X-rays.
A combination of many unresolved X-ray sources is thought to produce the X-ray background observed across the entire firmament. The X-ray continuum can arise from bremsstrahlung (braking radiation), blackbody radiation, synchrotron radiation, or the so-called inverse Compton scattering of low-energy photons by relativistic electrons, as well as collisions of fast protons with atomic electrons, and atomic recombination with or without additional electron transitions.
Radio Astronomy
Radio astronomy is a branch of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object occurred in 1932 when Karl Jansky observed radiation from the Milky Way at the Bell Telephone Laboratories. Subsequent observations have identified a number of different sources of radio emission. These include stars and galaxies, but also entirely new classes of objects such as radio galaxies, quasars, and pulsars. Radio astronomy has also been used to discover cosmic microwave background radiation, which is considered evidence for the Big Bang theory.
Radio astronomy is performed with large radio antennas, called radio telescopes, which are used either singly or connected in multiples. By using interferometry, radio astronomy can achieve high angular resolution because the resolving power of an interferometer is determined by the distance between its components, not by the size of its components.
Radio astronomers use various techniques to observe objects in the radio spectrum. They simply point their instruments at a high-energy radio source to analyze its emission. To create an image of a region of the sky in more detail, they take multiple overlapping scans and assemble them into a mosaic image. The type of instrument used depends on the strength of the signal and the level of detail required.
However, observations from the Earth’s surface are limited to wavelengths that can penetrate the atmosphere. At low frequencies or long wavelengths, the Earth’s ionosphere limits transmission because it reflects waves below a certain frequency. On the other hand, water vapor interferes with radio astronomy at higher frequencies. Therefore, people like to build radio observatories at very high, dry locations so that the water vapor content in the line of sight remains minimal. Finally, transmitting equipment on Earth can cause high-frequency interference. For this reason, radio observatories are best built in remote locations.
The difficulty of achieving high resolutions with single radio telescopes led to radio interferometry, which was developed in 1946 by British radio astronomer Martin Ryle and Australian engineers, radio physicists, and radio astronomers Joseph Lade Pawsey and Ruby Payne-Scott. It is based on superimposing images from two or more spatially distant sources.
Modern radio interferometers consist of widely separated radio telescopes observing the same object, connected by a coaxial cable, waveguide, optical fiber, or other types of transmission
lines. Not only does this increase the overall signal, but it can also be used in a process called ‘aperture synthesis’ or ‘synthesis imaging’ to greatly increase resolution. This technique works by superimposing (interfering) the signal waves from the different telescopes on the principle that waves coincident with the same phase add up, while two waves with opposite phases cancel each other out. This creates a combined telescope that is the size of the most widely spaced antennas in the array.
To produce a high-quality image, multiple and different distances between telescopes are required (the projected distance between two telescopes, as seen from the radio source, is called the ‘baseline’). As many different baselines as possible are needed to obtain good quality images. For example, the Very Large Array (VLA) has 27 telescopes that simultaneously provide 351 independent baselines.
Since the 1970s, improvements in the stability of radio telescope receivers have made it possible to combine telescopes from around the world—and even from Earth orbit—to perform interferometry with very long baselines. Instead of physically connecting the antennas, the data received at each antenna is paired with timing information, usually from a local atomic clock, and then stored for later analysis. At that later time, the data is correlated with data from other antennas recorded in a similar manner to produce the resulting image. Using this method, it is possible to produce an antenna that is effectively the size of the Earth. Because of the large distances between telescopes, very high angular resolutions can be achieved, greater than in any other field of astronomy.
The Beacon: Hard Science Fiction Page 22