Do Extraterrestrial Water and Sugar Justify a Manned Mission to the Outer Space?
Water vapour on Jupiter’s moon Europa; extraterrestrial ribose & RNA world; and Voyager 2 leaving the solar system — Astronomy November Briefing
Extraterrestrial water and sugars
Water and sugar are among the most fundamental ingredients of life. In November 2019, water vapour was detected on Europa — the sixth-closest moon of Jupiter discovered in 1610 (NASA; Nature Astronomy).
Extraterrestrial water has also been identified within other celestial bodies, most notably on Mars and Enceladus — one of the Saturn moons investigated by the Cassini-Huygens spacecraft.
It is not only water though.
Intriguingly, also extraterrestrial ribose, arabinose, xylose, and lyxose were now identified within the Murchison meteorite that fell to Earth in 1969 (CNN; Proceedings of the National Academy of Sciences; NASA).
Remarkably, one of the origin-of-life hypotheses states that an RNA world existed at the earliest point of the Earth’s history. First, a primordial soup gave rise to free-floating sugars, amino acids, and nucleotides. Second, some nucleotides were assembling with one another. They were dissociating quickly from one another, yet some nucleotides chains prevailed (for instance, their dissociation energy could have been smaller than their assembly energy). Much in this way, an RNA auto-catalytic cycle was established, in which RNA molecules catalysed (i.e., they sped up the reaction of) their own production. Third, some amino acids or rudimentary amino-acid chains (i.e., proteins) might have assembled around RNA and assisted its auto-catalytic cycle. Fourth, a protocell might have developed around such RNA molecules, encapsulating and protecting them from the environment.
Due to DNA’s greater stability, DNA overtook RNA’s function as genetic data storage over time.
The discovery of extraterrestrial ribose is therefore of paramount importance, hinting at a possibility that either elementary (RNA-based) or complex life forms (protein, DNA, and RNA-based) may exist beyond our planet and the solar system.
Is the astronaut life to die for?
Would these discoveries justify a manned journey to explore deep space?
A new study in JAMA Network Open (2019) provides novel evidence that astronauts experiencing weightlessness suffer from impaired cerebral blood flow and are thus prone to thrombosis (CNN). According to the Centers for Disease Control and Prevention (CDC), blood clots pose a serious health risk to long-distance travellers on Earth, and the longest commercial flight has yet to exceed 20 hours. Imagine flying for months or years in zero or artificial gravity.
With more and more disease symptoms of space travel becoming now apparent, how risky is a deep-space mission?
It is not only blood clots but also an elevated cancer risk that would make a manned trip beyond the close proximity of the Earth unfeasible. A 2018 study showed that energetic heavy ions, more prevalent in deep space but not low-orbit Earth, damage the gastrointestinal (GI) track by promoting cell senescence in mice (Proceedings of the National Academy of Sciences). Senescence is a phenomenon in which a cell ceases to proliferate; it does not die but enters a dormant state, which may be detrimental to the local homeostasis as the gut is a highly-proliferative organ. Furthermore, ionising radiation is known to cause DNA damage which is one of the direct causes of cancer (consult this Georgetown University Medical Center press release for more details; cnet.com also reported on this story).
Would humanity be capable of reproducing in deep space?
A study published in Biomedical and Environmental Sciences (2013) points to the fact that simulated microgravity as well as irradiation may cause a type of cell death called apoptosis in murine spermatogenic cells. In 2005, Reproductive Medicine and Biology reported that human sperm is slower under microgravity, but ever since data on the physiology of human sperm under microgravity has been scarce. One way to circumvent the issue of a possible damage to male reproductive cells would be to allow female astronauts to reproduce without men. Data presented in mid-2019 by Dr Montserrat Boada Palá at the European Society of Human Reproduction and Embryology (ESHRE) suggests that sperm exposed to zero gravity did not differ from control sperm cells (Guardian). In September 2019, a study in Scientific Reports showed evidence that the reproductive organs of mice housed at the low-orbit International Space Station (ISS) remained intact after 35 days in space; remarkably, they were also capable of producing healthy offspring.
Although biobanks with frozen sperm may be established to address the reproduction issue in the outer space, remaining physically and mentally fit is a far more complex issue. Mental health deterioration (anxiety), learning impairment, and memory loss are to be expected due to low-dose neutron radiation, according to a 2019 study from eNeuro (CNN also reported on this).
An in-depth explanation of the physiology of living off the Earth has recently been provided at the Physiological Society’s Presidential Lecture by the NASA astronaut and scientist James A. Pawelczyk (7 September 2019, Royal Institution in London).
The Voyagers have now entered a beautiful, unchartered territory
We have yet to acquire the technology to safely leave our solar system and survive. Before that happens, two beacons we created in late 1970 have been teaching us about the outskirts of the heliosphere.
Voyager 1 and Voyager 2 — two unmanned spacecrafts that left our solar system in 2012 and 2018, respectively — are transmitting data up to this very moment.
The analysis of their data reveals the nature of the border between the heliosphere and the interstellar space, referred to as a heliopause (see chart above). The heliosphere medium is defined as solar wind, or a hot, low-density plasma. The interstellar space is in turn viewed as cold, high-density plasma, and it has hitherto been a matter of debate how the border between the two looks like.
It was thought that the solar wind would gradually diminish in intensity the farther away from the sun it is. Nonetheless, the Voyager data confirms a rather hard border exists between the two media. This finding is crucial in understanding other solar systems but also sheds light on the anatomy of our own heliosphere (CNN; Nature Astronomy; phys.org; SciShow News).
I would typically include here a call-to-action.
Instead, I will leave here an open question to consider:
What if the next interstellar mission finds another Earth?
