The previously unreconciled acceleration of the interstellar object ‘Oumuamua is due to the production of hydrogen gas from ice reserves, suggests a study published in Nature this week.

‘Oumuamua is the first known interstellar object to be monitored travelling through our Solar System, having originated outside the Solar System. It displays a small non-gravitational acceleration typically associated with the release of trapped gas from a material, as seen in comets. However, it displays no further typical tracers of cometary activity such as a ‘tail’ of dust or gas. These seemingly contradictory observations have made it difficult for researchers to precisely define the nature of ‘Oumuamua.

In a model developed by Jennifer Bergner and Darryl Seligman, the acceleration of ‘Oumuamua is attributed to the release of trapped molecular hydrogen from within the object. This hydrogen has been formed through energetic processing of water-rich ice as the body passed close to the Sun, and is subsequently released from the object, slightly bending its path through our Solar System. Such reactions have been demonstrated in existing experimental work, showing that molecular hydrogen is known to be produced and subsequently expelled under such conditions.

Importantly, this model helps us understand ‘Oumuamua’s unusual properties without requiring further fine-tuning. The findings support previous theories that ‘Oumuamua may have originated as an icy planetesimal — a small object formed during the early stages of planet formation — similar to Solar System comets.

The zebra finch’s ability to transition between syllables in its courtship songs is driven by the influence of the thalamus region of the brain and a specific set of neurons in another region of the brain associated with birdsong, according to a paper in Nature. The findings highlight the role of the thalamus in controlling complex behaviour.

The thalamus has been shown to play a central role in generating simple trained movements in animals, as inputs from the thalamus are necessary to string short movements together into longer sequences. Male zebra finches (Taeniopygia guttata) practice singing by copying their father’s song, which consists of a sequence of two to seven syllables, each distinct and behaviourally meaningful. However, the mechanisms underlying the motor commands that generate these sequences are unclear.

Michael Long and colleagues studied how neurons in different brain areas work together to learn and produce these courtship songs. The authors used brain imaging to monitor activity in finch brains while they performed their songs in response to seeing their preferred female partners. The authors also used a stimulation electrode implanted in the brain to administer an electrical current at specific moments during the song. Stimulation of a small structure in the thalamus known as nucleus uvaeformis (Uva) showed that this region connects with a set of nerve cells in the brain region called HVC. These nerve cells become very active just before the start of syllables.

These findings have implications for understanding how complex behaviours are generated from combinations of simpler movements; similar arrangements have also been suggested to coordinate human speech and breathing.

Uracil, one of the building blocks necessary to form RNA, and vitamin B3, an important cofactor for metabolism in terrestrial life, have been detected in samples collected from the near-Earth asteroid Ryugu, according to a paper published in Nature Communications. The findings suggest that nucleobases, such as uracil, have an extra-terrestrial origin and were delivered to Earth by carbon-rich meteorites.

The Hayabusa2 spacecraft collected samples from two different landing sites on Ryugu, which are thought to have had different histories, and returned them to Earth in December 2020.

Yasuhiro Oba and colleagues used newly developed small-scale analytical techniques to analyse samples from both landing sites of the asteroid Ryugu. They detected uracil, niacin (vitamin B3), and other organic molecules thought to be important for the synthesis of further complex organic molecules. These molecules may have eventually led to the emergence of the first life on Earth, the authors suggest. They had previously been found by the same research team in meteorites found on Earth, but their detection in pristine samples returned from Ryugu suggests an extra-terrestrial origin.

The authors suggest that these compounds could have been generated by photochemical reactions in interstellar ice, which later led to their incorporation into asteroids as the solar system formed. UV and cosmic radiation may have further altered them over millions of years. The delivery of these compounds to Earth by meteorite impact could have played an important role in the emergence of genetic functions of early life, the authors suggest.