One model proposed that the universe started from a small, hot, dense plasma billions of years ago and has been expanding ever since — the Big Bang model; another suggested that the cosmos stands still and that the changes astronomers see are mostly local — the steady state model.

Arno Penzias and Robert Wilson accidentally discovered the cosmic microwave background radiation (CMB), a fossil from the early universe predicted to exist by George Gamow, Ralph Alpher, and Robert Herman in their Big Bang model.

(Alpher and Herman published a lovely account of the history here.) The CMB is a bath of microwave photons that permeates the whole of space, a remnant from the epoch when the first hydrogen atoms were forged, some 400,000 years after the bang.

Confirming the general outline of the Big Bang model changed our cosmic view?

The universe, like you and me, has a history, a past waiting to be explored.

There is a simple relation that connects the age of the universe and its temperature, measured in terms of the temperature of photons (the particles of visible light and other forms of invisible radiation).

The universe was filled with a primordial soup of particles: protons, neutrons, electrons, photons, and neutrinos, the ghostly particles that cross planets and people unscathed?

Long before Alexandria became the center of Egyptian trade, there was Thônis-Heracleion.

Pinned beneath fallen temple stones is a surprisingly intact Egyptian military vessel from the second century BCE, and researchers have excavated a large cemetery from the fourth century BCE.

Credit: Egyptian Ministry of Tourism and Antiques.

(The other, Canopus, was discovered in 1999.) For millennia, experts assumed Thônis-Heracleion were two different lost cities, but it's now known that Thônis is simply the city's Egyptian name, while Heracleion is its Greek name.

This all ended when the Egyptian dynasty created by Ptolemy set out to establish Alexandria as Egypt's center.

Gold mask found in a submerged Greek cemetery.Credit: Egyptian Ministry of Tourism and Antiques.

The newly discovered ship was found beneath 16 feet of hard clay, "thanks to cutting-edge prototype sub-bottom profiler electronic equipment," says Ayman Ashmawy of the Egyptian Ministry of Tourism and Antiques.

Like its dually-named city, it's an amalgam of Greek and Egyptian ship-building techniques.

On the other hand, it was built to be rowed, and some of its wood was reused lumber, signature traits of Egyptian boat design.

A statement by the Egyptian Ministry of Tourism and Antiques describes its significance, as reported by Reuters:.

Spacecraft from three of the world's space agencies reached Mars this year.

In February, the United Arab Emirates' Hope space probe entered the Martian orbit, where it is studying the planet's weather cycles.

And in May, China successfully landed its Zhurong rover on the Martian surface, becoming the second nation to ever do so.

The timing was no coincidence: once every two years, Earth and Mars come especially close together because their orbits are "at opposition," which is when the Earth-Mars distance is smallest during the 780-day synodic period.

The handful of spacecraft currently exploring the Martian surface and atmosphere are scheduled to conduct their experiments for periods ranging from months to years.

Photo of Martian surface taken by the Perseverance roverNASA/JPL-Caltech.

If all goes well, an Airbus spacecraft dubbed the Earth Return Orbiter (ERO) will carry the samples back to Earth in 2031.

It would be the first time a space mission has returned Martian matter to Earth.

In 2023, Roscosmos and the European Space Agency plan to land their Rosalind Franklin rover on the Martian surface, where it will drill into rock and analyze soil composition for signs of past — or possibly present — alien life.

The joint mission is part of a long-term Mars project that began in 2016.

In 2024, JAXA also plans to launch a uniquely bold interplanetary mission that will involve sending a probe to orbit Mars, landing on the Martian moon Phobos, collecting surface samples, and then returning those samples to Earth in 2029

JAXA says the mission has two main objectives: (1) to investigate whether the Martian moons are captured asteroids or fragments that coalesced after a giant impact with Mars; and (2) to clarify the mechanisms controlling the surface evolution of the Martian moons and Mars

As the International Space Station project is coming to a close, China is in the process of building its own space station; earlier this year it launched into orbit the first part of its station, which will take 10 more missions to assemble

Elon Musk's California-based aerospace company has its sights on two Mars voyages: a cargo-only mission in 2022 and a human mission by 2026

In 2014, the Indian Space Research Organization executed its first interplanetary trip with its Mars Orbiter Mission

It marked the first time an Asian nation reached Martian orbit and also the first time a nation successfully reached the Red planet on its maiden voyage

India has plans for a follow-up Mars Orbiter Mission 2, but it remains unclear when that will occur and what the mission will entail

In February, the chief of the Indian Space Research Organisation said the nation would only launch a Mars mission after Chandrayaan-3, India's upcoming mission to the Moon, which is expected to launch in 2022