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Getting ahead
The back pages Almost the last word Clouds gather in Kenya. But why does the air smell fresher before a storm?
Lighter Earth We have sent a large number of spacecraft and satellites into space. This must reduce the mass of the planet, albeit by a small amount. Does this reduction affect Earth’s gravity with respect to the sun and moon?
Herman D’Hondt Sydney, Australia Most of a launched rocket falls back to Earth, and the used fuel also stays within the atmosphere. Only a small part of the rocket actually makes it into orbit. For example, the 2800-tonne Saturn V (still the most powerful rocket ever) was able to put 118 tonnes into orbit – just over 4 per cent of its launch mass. Also, spacecraft in orbit are still part of Earth. Even in geosynchronous orbit at an altitude of 37,000 kilometres, they contribute to the planet’s gravity just as much as they did when they were standing on the launch pad. The main point, though, is that all of these figures are so small compared with the mass of Earth itself that the effect is almost completely irrelevant to the planet’s gravity. 54 | New Scientist | 18 May 2019
IAN FORSYTH/GETTY
Anthony Roberts Rushden, Northamptonshire, UK Bearing in mind that much of the stuff we send into space falls back down again, only a few hundred tonnes of spacecraft have actually escaped Earth’s gravity since the first space programmes began. This is tiny compared with the quantity of hydrogen and other gases that escape continuously into space from the upper atmosphere. This has been estimated at between 30,000 and 65,000 tonnes per year. Earth also gains about 40,000 tonnes per year in the form of meteorites and space dust. Overall, though, the planet gets slightly lighter each year. But this only amounts to around a trillionth of a per cent, as Earth is very, very heavy at 5.97 × 1024 kilograms.
expected between family and close friends, but even then, I just give a hug. I am not about to find out whether being licked by an animal or kissed by a human is more dangerous. I will keep my distance, and keep washing my hands.
This week’s new questions: What causes the fresh smell we experience just before the onset of a storm or shower of rain, which is especially noticeable after an extended dry spell? Colin Francombe, Nanyuki, Kenya Why is it that the same foods or drinks taste pleasant to some people and horrible to others? Rachel Mckeown, Aberfan, Merthyr Tydfil, UK
Jamie Barrett Rickmansworth, Hertfordshire, UK Although the mass of Earth itself decreases slightly when a satellite is sent into orbit, the total mass of Earth and its satellites stays the same. Assuming satellites are distributed more or less evenly around any given orbit, this also means the position of the centre of mass of Earth and its satellites doesn’t change, so Earth’s gravity with respect to the sun and moon isn’t affected. Sending spacecraft to other planets or beyond this solar system does reduce the mass of Earth and its satellites, but this is probably too small to have any effect.
Intimate contact From a pathogenic perspective, which is more dangerous, to be licked by an animal or kissed by a human?
Anna Butcher Brookton, Western Australia I was once told that “germs don’t fly, they hitch-hike”.
Many animals can carry pathogens that are transmissible to humans, so I am not at all keen on being licked by any animal. The dogs that work on our farm – two hard-working, affectionate kelpies – are washed and wormed regularly, but they aren’t allowed to lick me. I still can’t get over the fact that they see animal remains as attractive and are possible carriers of the hydatid tapeworm (Echinococcus granulosus), which can cause serious illness. Sheep, cattle and goats can be infected with the bacteria that cause Q fever (Coxiella burnetii ) and cats can be infected with Toxoplasma gondii. Both are transmissible to humans, though by means other than licking or kissing. As for humans, I am averse to being kissed by strangers. My Italian heritage means that an informal hug and kiss greeting is
Henry O’Regan Harpenden, Hertfordshire, UK It depends on personal hygiene. Animals, of course, lick and eat items that have been exposed to a wider variety of pathogens. Humans are usually much more hygienic when it comes to these things. However, some of us are more strict with hygiene than others. The question of whether it is more dangerous to be licked by an animal or kissed by a human must be taken on a case-by-case basis.
Getting ahead My fringe seems to grow faster than the rest of my hair. Is this just because I notice it more, or does hair grow at different rates on different parts of the head?
Jackie Jones Brighton, UK I have had a fringe for most of my life. It is very noticeable when it grows by 10 millimetres, and I have to cut it. But I don’t notice the rest of my hair so much, so I think it is a question of perception, rather than different growth rates. Incidentally, my hair hasn’t grown more slowly with age (I am now 70), but each hair follicle dies after a shorter time than it did when I was younger. The hair on the rest of my head, which is waist length, is now about 150 millimetres shorter than it was about 10 years ago.
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms
Lighter Earth We have sent a large number of spacecraft and satellites into space. This must reduce the mass of the planet, albeit by a small amount. Does this reduction affect Earth’s gravity with respect to the sun and moon?
Herman D’Hondt Sydney, Australia Most of a launched rocket falls back to Earth, and the used fuel also stays within the atmosphere. Only a small part of the rocket actually makes it into orbit. For example, the 2800-tonne Saturn V (still the most powerful rocket ever) was able to put 118 tonnes into orbit – just over 4 per cent of its launch mass. Also, spacecraft in orbit are still part of Earth. Even in geosynchronous orbit at an altitude of 37,000 kilometres, they contribute to the planet’s gravity just as much as they did when they were standing on the launch pad. The main point, though, is that all of these figures are so small compared with the mass of Earth itself that the effect is almost completely irrelevant to the planet’s gravity. 54 | New Scientist | 18 May 2019
IAN FORSYTH/GETTY
Anthony Roberts Rushden, Northamptonshire, UK Bearing in mind that much of the stuff we send into space falls back down again, only a few hundred tonnes of spacecraft have actually escaped Earth’s gravity since the first space programmes began. This is tiny compared with the quantity of hydrogen and other gases that escape continuously into space from the upper atmosphere. This has been estimated at between 30,000 and 65,000 tonnes per year. Earth also gains about 40,000 tonnes per year in the form of meteorites and space dust. Overall, though, the planet gets slightly lighter each year. But this only amounts to around a trillionth of a per cent, as Earth is very, very heavy at 5.97 × 1024 kilograms.
expected between family and close friends, but even then, I just give a hug. I am not about to find out whether being licked by an animal or kissed by a human is more dangerous. I will keep my distance, and keep washing my hands.
This week’s new questions: What causes the fresh smell we experience just before the onset of a storm or shower of rain, which is especially noticeable after an extended dry spell? Colin Francombe, Nanyuki, Kenya Why is it that the same foods or drinks taste pleasant to some people and horrible to others? Rachel Mckeown, Aberfan, Merthyr Tydfil, UK
Jamie Barrett Rickmansworth, Hertfordshire, UK Although the mass of Earth itself decreases slightly when a satellite is sent into orbit, the total mass of Earth and its satellites stays the same. Assuming satellites are distributed more or less evenly around any given orbit, this also means the position of the centre of mass of Earth and its satellites doesn’t change, so Earth’s gravity with respect to the sun and moon isn’t affected. Sending spacecraft to other planets or beyond this solar system does reduce the mass of Earth and its satellites, but this is probably too small to have any effect.
Intimate contact From a pathogenic perspective, which is more dangerous, to be licked by an animal or kissed by a human?
Anna Butcher Brookton, Western Australia I was once told that “germs don’t fly, they hitch-hike”.
Many animals can carry pathogens that are transmissible to humans, so I am not at all keen on being licked by any animal. The dogs that work on our farm – two hard-working, affectionate kelpies – are washed and wormed regularly, but they aren’t allowed to lick me. I still can’t get over the fact that they see animal remains as attractive and are possible carriers of the hydatid tapeworm (Echinococcus granulosus), which can cause serious illness. Sheep, cattle and goats can be infected with the bacteria that cause Q fever (Coxiella burnetii ) and cats can be infected with Toxoplasma gondii. Both are transmissible to humans, though by means other than licking or kissing. As for humans, I am averse to being kissed by strangers. My Italian heritage means that an informal hug and kiss greeting is
Henry O’Regan Harpenden, Hertfordshire, UK It depends on personal hygiene. Animals, of course, lick and eat items that have been exposed to a wider variety of pathogens. Humans are usually much more hygienic when it comes to these things. However, some of us are more strict with hygiene than others. The question of whether it is more dangerous to be licked by an animal or kissed by a human must be taken on a case-by-case basis.
Getting ahead My fringe seems to grow faster than the rest of my hair. Is this just because I notice it more, or does hair grow at different rates on different parts of the head?
Jackie Jones Brighton, UK I have had a fringe for most of my life. It is very noticeable when it grows by 10 millimetres, and I have to cut it. But I don’t notice the rest of my hair so much, so I think it is a question of perception, rather than different growth rates. Incidentally, my hair hasn’t grown more slowly with age (I am now 70), but each hair follicle dies after a shorter time than it did when I was younger. The hair on the rest of my head, which is waist length, is now about 150 millimetres shorter than it was about 10 years ago.
Want to send us a question or answer?
Email us at [email protected] Questions should be about everyday science phenomena Full terms and conditions at newscientist.com/lw-terms