Scientist Plannig Now for a Asteroid flyby a Decade away.

   Apophis Asteroid

On April 13, 2029, a speck of light will streak across the sky getting brighter and faster. At one point it will travel more than the width of the full Moon within a minute and it will get as bright as the stars in the Little Dipper. But it won’t be a satellite or an airplane—it will be a 340-meter-wide near-Earth asteroid called 99942 Apophis that will cruise harmlessly by Earth, about 19,000 miles (31,000 km) above the surface. That’s within the distance that some of our spacecraft that orbit Earth.

This animation shows the distance between the Apophis asteroid and Earth at the time of the asteroid’s closest approach. The blue dots are the many man-made satellites that orbit our planet, and the pink represents the International Space Station. Credit: Marina Brozović/JPL

The international asteroid research community couldn’t be more excited.

This week at the 2019 Planetary Defense Conference in College Park, Maryland, scientists are gathering to discuss observation plans and science opportunities for the celestial event still a decade away. During a session on April 30, scientists will discuss everything from how to observe the event to hypothetical missions we could send out to the asteroid.

"The Apophis close approach in 2029 will be an incredible opportunity for science,” said Marina Brozović, a radar scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, who works on radar observations of near-Earth objects (NEOs). “We’ll observe the asteroid with both optical and radar telescopes. With radar observations, we might be able to see surface details that are only a few meters spotted small asteroids, on the order of 5-10 meters, flying by Earth at a similar distance, asteroids the size of Apophis are far fewer in number and so do not pass this close to Earth as often.

The asteroid, looking like a moving star-like point of light, will first become visible to the naked eye in the night sky over the southern hemisphere, flying above Earth from the east coast to the west coast of Australia. It will be mid-morning on the East Coast of the United States when Apophis is above Australia. It will then cross the Indian Ocean, and by the afternoon in the eastern U.S. it will have crossed the equator, still moving west, above Africa. At closest approach, just before 6 p.m. EDT, Apophis will be over the Atlantic Ocean – and it will move so fast that it will cross the Atlantic in just an hour. By 7 p.m. EDT, the asteroid will have crossed over the United States.

This animation shows the path along Earth where Apophis will be visible on April 13, 2029. As the asteroid passes over the Atlantic ocean, its path briefly turns from red to grey – that is the moment of closest approach. After closest approach, the asteroid will move into the daytime sky and will no longer be visible. Credit: Marina Brozović/JPL

A team of astronomers at the Kitt Peak National Observatory discovered Apophis in June 2004. The astronomers were only able to detect the asteroid for two days before technical and weather issues prevented further observations. Luckily, another team rediscovered the asteroid at the Siding Spring Survey in Australia later that year. The observations caused quite a stir—initial orbital calculations revealed that the asteroid had a 2.7% chance of impacting Earth in 2029. Fortunately, additional observations refined the orbit and completely ruled out that possibility.

Since its discovery, optical and radar telescopes have tracked Apophis as it continues on its orbit around the Sun, so we know its future trajectory quite well. Current calculations show that Apophis still has a small chance of impacting Earth, less than 1 in 100,000 many decades from now, but future measurements of its position can be expected to rule out any possible impacts.

The most important observations of Apophis will occur in 2029, when asteroid scientists around the world will have an opportunity to conduct a close-up study of the Apophis’s size, shape, composition, and possibly even its interior.

At the conference, scientists will discuss questions like “How will Earth’s gravity affect the asteroid as it passes by?”, “Can we use Apophis’ flyby to learn about an asteroid’s interior?”, and “Should we send a spacecraft mission to Apophis?”

“We already know that the close encounter with Earth will change Apophis’ orbit, but our models also show the close approach could change the way this asteroid spins, and it is possible that there will be some surface changes, like small avalanches,” said Davide Farnocchia, an astronomer at JPL’s Center for Near Earth Objects Studies (CNEOS), who is co-chairing the April 30 session on Apophis with Brozović.

“Apophis is a representative of about 2,000 currently known Potentially Hazardous Asteroids (PHAs),” said Paul Chodas, director of CNEOS. “By observing Apophis during its 2029 flyby, we will gain important scientific knowledge that could one day be used for planetary defense.”

New Hubble telescope's data show that Universe is Expanding weirdly.

Astronomers using NASA's Hubble Space Telescope say they have crossed an important threshold in revealing a discrepancy between the two key techniques for measuring the universe's expansion rate. The recent study strengthens the case that new theories may be needed to explain the forces that have shaped the cosmos.

This is a ground-based telescope's view of the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The inset image, taken by the Hubble Space Telescope, reveals one of many star clusters scattered throughout the dwarf galaxy. The cluster members include a special class of pulsating star called a Cepheid variable, which brightens and dims at a predictable rate that corresponds to its intrinsic brightness. Once astronomers determine that value, they can measure the light from these stars to calculate an accurate distance to the galaxy. When the new Hubble observations are correlated with an independent distance measurement technique to the Large Magellanic Cloud (using straightforward trigonometry), the researchers were able to strengthen the foundation of the so-called "cosmic distance ladder." This "fine-tuning" has significantly improved the accuracy of the rate at which the universe is expanding, called the Hubble constant.

Credits: NASA, ESA, A. Riess (STScI/JHU) and Palomar Digitized Sky Survey

As the team's measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe's expansion. Those measurements were made by Planck, which maps the cosmic microwave background, a relic afterglow from 380,000 years after the big bang.

The measurements have been thoroughly vetted, so astronomers cannot currently dismiss the gap between the two results as due to an error in any single measurement or method. Both values have been tested multiple ways.

"This is not just two experiments disagreeing," Riess explained. "We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don't agree, there becomes a very strong likelihood that we're missing something in the cosmological model that connects the two eras."

How the new study was done

Astronomers have been using Cepheid variables as cosmic yardsticks to gauge nearby intergalactic distances for more than a century. But trying to harvest a bunch of these stars was so time-consuming as to be nearly unachievable. So, the team employed a clever new method, called DASH (Drift And Shift), using Hubble as a "point-and-shoot" camera to snap quick images of the extremely bright pulsating stars, which eliminates the time-consuming need for precise pointing.

  This illustration shows the three basic steps astronomers use to calculate how fast the universe expands over time, a value called the Hubble constant. All the steps involve building a strong "cosmic distance ladder," by starting with measuring accurate distances to nearby galaxies and then moving to galaxies farther and farther away. This "ladder" is a series of measurements of different kinds of astronomical objects with an intrinsic brightness that researchers can use to calculate distances. Among the most reliable for shorter distances are Cepheid variables, stars that pulsate at predictable rates that indicate their intrinsic brightness. Astronomers recently used the Hubble Space Telescope to observe 70 Cepheid variables in the nearby Large Magellanic Cloud to make the most precise distance measurement to that galaxy. Astronomers compare the measurements of nearby Cepheids to those in galaxies farther away that also include another cosmic yardstick, exploding stars called Type Ia supernovas. These supernovas are much brighter than Cepheid variables. Astronomers use them as "milepost markers" to gauge the distance from Earth to far-flung galaxies. Each of these markers build upon the previous step in the "ladder." By extending the ladder using different kinds of reliable milepost markers, astronomers can reach very large distances in the universe. Astronomers compare these distance values to measurements of an entire galaxy's light, which increasingly reddens with distance, due to the uniform expansion of space. Astronomers can then calculate how fast the cosmos is expanding: the Hubble constant.

Credits: NASA, ESA and A. Feild (STScI)

"When Hubble uses precise pointing by locking onto guide stars, it can only observe one Cepheid per each 90-minute Hubble orbit around Earth. So, it would be very costly for the telescope to observe each Cepheid," explained team member Stefano Casertano, also of STScI and Johns Hopkins. "Instead, we searched for groups of Cepheids close enough to each other that we could move between them without recalibrating the telescope pointing. These Cepheids are so bright, we only need to observe them for two seconds. This technique is allowing us to observe a dozen Cepheids for the duration of one orbit. So, we stay on gyroscope control and keep 'DASHing' around very fast."

The Hubble astronomers then combined their result with another set of observations, made by the Araucaria Project, a collaboration between astronomers from institutions in Chile, the U.S., and Europe. This group made distance measurements to the Large Magellanic Cloud by observing the dimming of light as one star passes in front of its partner in eclipsing binary-star systems.

The combined measurements helped the SH0ES Team refine the Cepheids' true brightness. With this more accurate result, the team could then "tighten the bolts" of the rest of the distance ladder that extends deeper into space.

The new estimate of the Hubble constant is 74 kilometers (46 miles) per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 74 kilometers (46 miles) per second faster, as a result of the expansion of the universe. The number indicates that the universe is expanding at a 9% faster rate than the prediction of 67 kilometers (41.6 miles) per second per megaparsec, which comes from Planck's observations of the early universe, coupled with our present understanding of the universe.

So, what could explain this discrepancy?

One explanation for the mismatch involves an unexpected appearance of dark energy in the young universe, which is thought to now comprise 70% of the universe's contents. Proposed by astronomers at Johns Hopkins, the theory is dubbed "early dark energy," and suggests that the universe evolved like a three-act play.

Astronomers have already hypothesized that dark energy existed during the first seconds after the big bang and pushed matter throughout space, starting the initial expansion. Dark energy may also be the reason for the universe's accelerated expansion today. The new theory suggests that there was a third dark-energy episode not long after the big bang, which expanded the universe faster than astronomers had predicted. The existence of this "early dark energy" could account for the tension between the two Hubble constant values, Riess said.

Another idea is that the universe contains a new subatomic particle that travels close to the speed of light. Such speedy particles are collectively called "dark radiation" and include previously known particles like neutrinos, which are created in nuclear reactions and radioactive decays.

Yet another attractive possibility is that dark matter (an invisible form of matter not made up of protons, neutrons, and electrons) interacts more strongly with normal matter or radiation than previously assumed.

But the true explanation is still a mystery.

Riess doesn't have an answer to this vexing problem, but his team will continue to use Hubble to reduce the uncertainties in the Hubble constant. Their goal is to decrease the uncertainty to 1%, which should help astronomers identify the cause of the discrepancy.

Gravitational Waves may help in detection of star colliding with BlackHole.

Gravitational waves may have just delivered the first sighting of a black hole devouring a neutron star. If confirmed, it would be the first evidence of the existence of such binary systems. The news comes just a day after astronomers had detected gravitational waves from a merger of two neutron stars for only the second time.

At 15:22:17 UTC on 26 April, the twin detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO)in the United States and the Virgo observatory in Italy reported a burst of waves of an unusual type. Astronomers are still analysing the data and doing computer simulations to interpret them.

But they are already considering the tantalizing prospect that they have made a long-hoped-for detection that could produce a wealth of cosmic information, from precise tests of the general theory of relativity to measuring the Universe’s rate of expansion. Astronomers around the world are also racing to observe the phenomenon using different types of telescope.

“I think that the classification is leaning towards neutron star–black hole” merger, says Chad Hanna, a senior member of LIGO’s data-analysis team and a physicist at Pennsylvania State University in University Park. But the signal was not very strong, which means that it could be a fluke. “I think people should get excited about it, but they should also be aware that the significance is much lower” than in many previous events, he says. LIGO and Virgo had previously caught gravitational waves — faint ripples in the fabric of space-time — from two types of cataclysmic event: the mergers of two black holes, and of two neutron stars. The latter are small but ultra-dense objects formed after the collapse of stars more massive than the Sun.

The latest event, provisionally labelled #S190426c, appears to have occurred around 375 megaparsecs (1.2 billion light-years) away, the LIGO–Virgo team calculated. The researchers have drawn a ‘sky map’, showing where the gravitational waves are most likely to have originated, and sent this information out as a public alert, so that astronomers around the world could begin searching the sky for light from the event. Matching gravitational waves to other forms of radiation in this way can produce much more information about the event than either type of data can alone.

Mansi Kasliwal, an astrophysicist at the California Institute of Technology in Pasadena, leads one of several projects designed to do this type of follow-up work, called Global Relay of Observatories Watching Transients Happen (GROWTH). Her team can commandeer robotic telescopes around the world. In this case, the researchers immediately started up one in India, where it was night time when the gravitational waves arrived. “If weather cooperates, I think in less than 24 hours we should have coverage in almost the entire sky map,” she says.

Two at once

Astronomers were already working in overdrive when they spotted the potential black hole–neutron star merger. At 08:18:26 UTC on 25 April, another train of waves hit the LIGO’s detector in Livingston, Louisiana, and Virgo. (At the time, LIGO’s second machine, in Hanford, Washington, was briefly out of commission.)

That event was a clear-cut case of two merging neutron stars, Hanna says — nearly two years after the first historic discovery of such an event was made in August 2017.

Researchers can usually make such a call because the waves reveal the masses of the objects involved; objects roughly twice as heavy as the Sun are expected to be neutron stars. Based on the waves’ loudness, the researchers also estimated that the collision occurred some 150 megaparsecs (500 million light-years) away, says Hanna. That was around three times farther than the 2017 merger.

Iair Arcavi, an astrophysicist at Tel Aviv University who works on the Las Cumbres Observatory, one of GROWTH’s competitors, was in Baltimore, Maryland, to attend a conference called Enabling Multi-Messenger Astrophysics (EMMA) — the practice of observing these events in multiple wavelengths. The alert of the 25 April event came at 5:01 a.m. “I set it up to send me a text message, and it woke me up,” he says.

A storm of activity swept the meeting, with astronomers who would normally compete with each other exchanging information as they sat with their laptops around coffee tables. “We’re losing our minds over here at #EMMA2019”, tweeted astronomer Andy Howell.

But in this case, unlike many others, LIGO and Virgo were unable to significantly narrow down the direction in the sky that the waves came from. The researchers could say only that the signal was from a wide region that covers roughly one-quarter of the sky. They narrowed down the region slightly the day after.

Still, astronomers had well-honed machines for doing just this type of search, and the data they collected the following night should ultimately reveal the source, Kasliwal says. “if it existed in that region, there’s no way we would have missed it.”

In the 2017 neutron-star merger, the combination of observations in different wavelengths produced a stupendous amount of science. Two seconds after the event, an orbiting telescope had detected a burst of gamma rays — presumably released when the merged star collapsed into a black hole. And some 70 other observatories were busy for months, watching the event unfold across the electromagnetic spectrum, from radio waves to X-rays.

If the 26 April event is not a black hole–neutron star merger, it is probably also a collision of neutron stars, which would bring the total detections of this type up to three.

Long-sought system

But seeing a black hole sweep up a neutron star could produce a wealth of information that no other type of event can provide, says B. S. Sathyaprakash, a LIGO theoretical physicist at Pennsylvania State. To begin with, it confirms that these long-sought systems do exist, originating from binary stars of very different masses.

And the orbits the two objects trace in the final phases of their approach could be rather different from those seen with pairs of black holes. In the neutron star–black hole case, the more-massive black hole would twist space around it as it spins. “The neutron star will be swirled around in a spherical orbit rather than a quasi-circular orbit,” Sathyaprakash says. For this reason, “neutron star–black hole systems can be more powerful test beds for general relativity”, he says.

Moreover, the gravitational waves and the companion observations from astronomers could reveal what happens in the final phases before the merger. As tidal forces tear the neutron star apart, they could help astrophysicist solve a long-standing mystery: what state is matter in inside these ultra-compact objects.

The LIGO-Virgo collaboration began its current observing run on 1 April, and had expected to see roughly one merger of black holes per week and one of neutron stars per month. So far, those predictions have been met — the observatories have also seen several black-hole mergers this month. “This is just amazing,” says Kasliwal. “The Universe is fantastic.”